From 2f1343ec0e794bdad01fa683cb04f5c66cb332c5 Mon Sep 17 00:00:00 2001
From: John Wellbelove <github@wellbelove.co.uk>
Date: Sun, 5 Jul 2020 19:39:50 +0100
Subject: [PATCH 1/2] Initial string stream commit

---
 include/etl/basic_format_spec.h        |  22 +++
 include/etl/private/to_string_helper.h |  88 +++++++---
 include/etl/string_stream.h            | 180 ++++++++++++++++++++
 include/etl/to_string.h                |  58 ++++++-
 include/etl/to_u16string.h             |  60 ++++++-
 include/etl/to_u32string.h             |  60 ++++++-
 include/etl/to_wstring.h               |  60 ++++++-
 include/etl/u16string_stream.h         | 180 ++++++++++++++++++++
 include/etl/u32string_stream.h         | 180 ++++++++++++++++++++
 include/etl/wstring_stream.h           | 180 ++++++++++++++++++++
 test/test_string_stream.cpp            | 220 +++++++++++++++++++++++++
 test/test_u16string_stream.cpp         | 220 +++++++++++++++++++++++++
 test/test_u32string_stream.cpp         | 220 +++++++++++++++++++++++++
 test/test_wstring_stream.cpp           | 220 +++++++++++++++++++++++++
 test/vs2019/etl.vcxproj                |   8 +
 test/vs2019/etl.vcxproj.filters        |  24 +++
 16 files changed, 1946 insertions(+), 34 deletions(-)
 create mode 100644 include/etl/string_stream.h
 create mode 100644 include/etl/u16string_stream.h
 create mode 100644 include/etl/u32string_stream.h
 create mode 100644 include/etl/wstring_stream.h
 create mode 100644 test/test_string_stream.cpp
 create mode 100644 test/test_u16string_stream.cpp
 create mode 100644 test/test_u32string_stream.cpp
 create mode 100644 test/test_wstring_stream.cpp

diff --git a/include/etl/basic_format_spec.h b/include/etl/basic_format_spec.h
index ca3da502..6ffa332b 100644
--- a/include/etl/basic_format_spec.h
+++ b/include/etl/basic_format_spec.h
@@ -248,6 +248,28 @@ namespace etl
       return boolalpha_;
     }
 
+    //***************************************************************************
+    /// Equality operator.
+    //***************************************************************************
+    friend bool operator ==(const basic_format_spec& lhs, const basic_format_spec& rhs)
+    {
+      return (lhs.base_ == rhs.base_) &&
+             (lhs.width_ == rhs.width_) &&
+             (lhs.precision_ == rhs.precision_) &&
+             (lhs.upper_case_ == rhs.upper_case_) &&
+             (lhs.left_justified_ == rhs.left_justified_) &&
+             (lhs.boolalpha_ == rhs.boolalpha_) &&
+             (lhs.fill_ == rhs.fill_);
+    }
+
+    //***************************************************************************
+    /// Inequality operator.
+    //***************************************************************************
+    friend bool operator !=(const basic_format_spec& lhs, const basic_format_spec& rhs)
+    {
+      return !(lhs == rhs);
+    }
+
   private:
 
     uint_least8_t base_;
diff --git a/include/etl/private/to_string_helper.h b/include/etl/private/to_string_helper.h
index 8f83b73d..9f0b2234 100644
--- a/include/etl/private/to_string_helper.h
+++ b/include/etl/private/to_string_helper.h
@@ -88,7 +88,7 @@ namespace etl
     void add_boolean(const bool value,
                      TIString& str,
                      const etl::basic_format_spec<TIString>& format,
-                     const bool append)
+                     bool append)
     {
       typedef typename TIString::value_type type;
       typedef typename TIString::iterator   iterator;
@@ -136,7 +136,7 @@ namespace etl
     void add_integral(T value,
                       TIString& str,
                       const etl::basic_format_spec<TIString>& format,
-                      const bool append)
+                      bool append)
     {
       typedef typename TIString::value_type type;
       typedef typename TIString::iterator   iterator;
@@ -228,7 +228,7 @@ namespace etl
     void add_floating_point(T value,
                             TIString& str,
                             const etl::basic_format_spec<TIString>& format,
-                            const bool append)
+                            bool append)
     {
       typedef typename TIString::iterator   iterator;
       typedef typename TIString::value_type type;
@@ -289,22 +289,64 @@ namespace etl
     void add_pointer(const volatile void* value,
                      TIString& str,
                      const etl::basic_format_spec<TIString>& format,
-                     const bool append)
+                     bool append)
     {
       uintptr_t p = reinterpret_cast<uintptr_t>(value);
 
       return etl::private_to_string::add_integral(p, str, format, append);
     }
 
+    //***************************************************************************
+    /// Helper function for strings.
+    //***************************************************************************
+    template <typename TIString>
+    void add_string(const TIString& value,
+                    TIString& str,
+                    const etl::basic_format_spec<TIString>& format,
+                    bool append)
+    {
+      if (!append)
+      {
+        str.clear();
+      }
+
+      typename TIString::iterator start = str.end();
+
+      str.insert(str.end(), value.begin(), value.end());
+
+      etl::private_to_string::add_alignment(str, start, format);
+    }
+
+    //***************************************************************************
+/// Helper function for string views.
+//***************************************************************************
+    template <typename TSringView, typename TIString>
+    void add_string_view(const TSringView& value,
+                         TIString& str,
+                         const etl::basic_format_spec<TIString>& format,
+                         bool append)
+    {
+      if (!append)
+      {
+        str.clear();
+      }
+
+      typename TIString::iterator start = str.end();
+
+      str.insert(str.end(), value.begin(), value.end());
+
+      etl::private_to_string::add_alignment(str, start, format);
+    }
+
     //*********************************************************************************************************
 
     //***************************************************************************
     /// For booleans. Default format spec.
-    //***************************************************************************etl::basic_format_spec<TIString>
+    //***************************************************************************
     template <typename TIString>
     const TIString& to_string(const bool value,
                               TIString& str,
-                              const bool append = false)
+                              bool append = false)
     {
       etl::basic_format_spec<TIString> format;
 
@@ -320,7 +362,7 @@ namespace etl
     const TIString& to_string(const bool value,
                               TIString& str,
                               const etl::basic_format_spec<TIString>& format,
-                              const bool append = false)
+                              bool append = false)
     {
       etl::private_to_string::add_boolean(value, str, format, append);
 
@@ -333,7 +375,7 @@ namespace etl
     template <typename TIString>
     const TIString& to_string(const volatile void* value,
                               TIString& str,
-                              const bool append = false)
+                              bool append = false)
     {
       etl::basic_format_spec<TIString> format;
 
@@ -349,7 +391,7 @@ namespace etl
     const TIString& to_string(const volatile void* value,
                               TIString& str,
                               const etl::basic_format_spec<TIString>& format,
-                              const bool append = false)
+                              bool append = false)
     {
       etl::private_to_string::add_pointer(value, str, format, append);
 
@@ -364,7 +406,7 @@ namespace etl
     typename etl::enable_if<etl::is_integral<T>::value &&
                             etl::is_signed<T>::value &&
                             !etl::is_same<T, bool>::value>::value, const TIString& > ::type
-      to_string(const T value, TIString& str, const bool append = false)
+      to_string(const T value, TIString& str, bool append = false)
     {
       etl::basic_format_spec<TIString> format;
 
@@ -380,7 +422,7 @@ namespace etl
     typename etl::enable_if<etl::is_integral<T>::value &&
                             etl::is_signed<T>::value &&
                             !etl::is_same<T, bool>::value>::value, const TIString& > ::type
-      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, const bool append = false)
+      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, bool append = false)
     {
       etl::private_to_string::add_integral(int32_t(value), str, format, append);
 
@@ -394,7 +436,7 @@ namespace etl
     typename etl::enable_if<etl::is_integral<T>::value &&
                             etl::is_unsigned<T>::value &&
                             !etl::is_same<T, bool>::value>::value, const TIString& > ::type
-      to_string(const T value, TIString& str, const bool append = false)
+      to_string(const T value, TIString& str, bool append = false)
     {
       etl::basic_format_spec<TIString> format;
 
@@ -410,7 +452,7 @@ namespace etl
     typename etl::enable_if<etl::is_integral<T>::value &&
                             etl::is_unsigned<T>::value &&
                             !etl::is_same<T, bool>::value>::value, const TIString& > ::type
-      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, const bool append = false)
+      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, bool append = false)
     {
       etl::private_to_string::add_integral(uint32_t(value), str, format, append);
 
@@ -425,7 +467,7 @@ namespace etl
                             etl::is_signed<T>::value &&
                             !etl::is_same<T, bool>::value &&
                             !etl::is_same<T, int64_t>::value, const TIString&>::type
-      to_string(const T value, TIString& str, const bool append = false)
+      to_string(const T value, TIString& str, bool append = false)
     {
       etl::basic_format_spec<TIString> format;
 
@@ -442,7 +484,7 @@ namespace etl
                             etl::is_signed<T>::value &&
                             !etl::is_same<T, bool>::value &&
                             !etl::is_same<T, int64_t>::value, const TIString&>::type
-      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, const bool append = false)
+      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, bool append = false)
     {
       etl::private_to_string::add_integral(int32_t(value), str, format, append);
 
@@ -457,7 +499,7 @@ namespace etl
                             etl::is_unsigned<T>::value &&
                             !etl::is_same<T, bool>::value &&
                             !etl::is_same<T, uint64_t>::value, const TIString&>::type
-      to_string(const T value, TIString& str, const bool append = false)
+      to_string(const T value, TIString& str, bool append = false)
     {
       etl::basic_format_spec<TIString> format;
 
@@ -474,7 +516,7 @@ namespace etl
                             etl::is_unsigned<T>::value &&
                             !etl::is_same<T, bool>::value &&
                             !etl::is_same<T, uint64_t>::value, const TIString&>::type
-      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, const bool append = false)
+      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, bool append = false)
     {
       etl::private_to_string::add_integral(uint32_t(value), str, format, append);
 
@@ -489,7 +531,7 @@ namespace etl
                             etl::is_signed<T>::value &&
                             !etl::is_same<T, bool>::value &&
                             etl::is_same<T, int64_t>::value, const TIString&>::type
-      to_string(const T value, TIString& str, const bool append = false)
+      to_string(const T value, TIString& str, bool append = false)
     {
       etl::basic_format_spec<TIString> format;
 
@@ -506,7 +548,7 @@ namespace etl
                             etl::is_signed<T>::value &&
                             !etl::is_same<T, bool>::value &&
                             etl::is_same<T, int64_t>::value, const TIString&>::type
-      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, const bool append = false)
+      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, bool append = false)
     {
       etl::private_to_string::add_integral(int64_t(value), str, format, append);
 
@@ -521,7 +563,7 @@ namespace etl
                             etl::is_unsigned<T>::value &&
                             !etl::is_same<T, bool>::value &&
                             etl::is_same<T, uint64_t>::value, const TIString&>::type
-      to_string(const T value, TIString& str, const bool append = false)
+      to_string(const T value, TIString& str, bool append = false)
     {
       etl::basic_format_spec<TIString> format;
 
@@ -538,7 +580,7 @@ namespace etl
                             etl::is_unsigned<T>::value &&
                             !etl::is_same<T, bool>::value &&
                             etl::is_same<T, uint64_t>::value, const TIString&>::type
-      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, const bool append = false)
+      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, bool append = false)
     {
       etl::private_to_string::add_integral(uint64_t(value), str, format, append);
 
@@ -551,7 +593,7 @@ namespace etl
     //***************************************************************************
     template <typename T, typename TIString>
     typename etl::enable_if<etl::is_floating_point<T>::value, const TIString&>::type
-      to_string(const T value, TIString& str, const bool append = false)
+      to_string(const T value, TIString& str, bool append = false)
     {
       etl::basic_format_spec<TIString> format;
 
@@ -565,7 +607,7 @@ namespace etl
     //***************************************************************************
     template <typename T, typename TIString>
     typename etl::enable_if<etl::is_floating_point<T>::value, const TIString&>::type
-      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, const bool append = false)
+      to_string(const T value, TIString& str, const etl::basic_format_spec<TIString>& format, bool append = false)
     {
       etl::private_to_string::add_floating_point(value, str, format, append);
 
diff --git a/include/etl/string_stream.h b/include/etl/string_stream.h
new file mode 100644
index 00000000..7842c157
--- /dev/null
+++ b/include/etl/string_stream.h
@@ -0,0 +1,180 @@
+///\file
+
+/******************************************************************************
+The MIT License(MIT)
+
+Embedded Template Library.
+https://github.com/ETLCPP/etl
+https://www.etlcpp.com
+
+Copyright(c) 2020 jwellbelove
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files(the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions :
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+******************************************************************************/
+
+#ifndef ETL_STRING_STREAM_INCLUDED
+#define ETL_STRING_STREAM_INCLUDED
+
+///\ingroup string
+
+#include "platform.h"
+#include "cstring.h"
+#include "format_spec.h"
+#include "to_string.h"
+#include "string_view.h"
+
+namespace etl
+{
+  class string_stream
+  {
+  public:
+
+    typedef etl::format_spec         format_spec_type;
+    typedef etl::istring             istring_type;
+    typedef etl::istring::value_type value_type;
+
+    //*************************************************************************
+    /// Construct from text.
+    //*************************************************************************
+    explicit string_stream(etl::istring& text_)
+      : text(text_)
+    {
+    }
+
+    //*************************************************************************
+    /// Construct from text and format spec.
+    //*************************************************************************
+    string_stream(etl::istring& text_, etl::format_spec spec_)
+      : text(text_)
+      , spec(spec_)
+    {
+    }
+
+    //*************************************************************************
+    /// Set the format spec.
+    //*************************************************************************
+    void set_format(etl::format_spec spec_)
+    {
+      spec = spec_;
+    }
+
+    //*************************************************************************
+    /// Get a const reference to the format spec.
+    //*************************************************************************
+    const etl::format_spec& get_format() const
+    {
+      return spec;
+    }
+
+    //*************************************************************************
+    /// Get a reference to the current string.
+    //*************************************************************************
+    etl::istring& str()
+    {
+      return text;
+    }
+
+    //*************************************************************************
+    /// Get a const reference to the current string.
+    //*************************************************************************
+    const etl::istring& str() const
+    {
+      return text;
+    }
+
+    //*************************************************************************
+    /// Resets the stream to the supplied string.
+    //*************************************************************************
+    void str(const etl::istring::value_type* p)
+    {
+      text.assign(p);
+    }
+
+    //*************************************************************************
+    /// Resets the stream to the supplied string.
+    //*************************************************************************
+    void str(const etl::istring& is)
+    {
+      text.assign(is);
+    }
+
+    //*************************************************************************
+    /// Get the current size of the string.
+    //*************************************************************************
+    size_t size() const
+    {
+      return text.size();
+    }
+
+    //*************************************************************************
+    /// Stream operators.
+    //*************************************************************************
+    friend string_stream& operator <<(string_stream& ss, etl::format_spec spec)
+    {
+      ss.spec = spec;
+      return ss;
+    }
+
+    //*********************************
+    friend string_stream& operator <<(string_stream& ss, etl::string_view view)
+    {
+      etl::to_string(view, ss.text, ss.spec, true);
+      return ss;
+    }
+
+    //*********************************
+    friend string_stream& operator <<(string_stream& ss, etl::istring::const_pointer p)
+    {
+      etl::string_view view(p);
+      ss << view;
+      return ss;
+    }
+
+    //*********************************
+    friend string_stream& operator <<(string_stream& ss, const etl::istring& text)
+    {
+      etl::to_string(text, ss.text, ss.spec, true);
+      return ss;
+    }
+
+    //*********************************
+    template <size_t SIZE>
+    friend string_stream& operator <<(string_stream& ss, const etl::string<SIZE>& text)
+    {
+      const etl::istring& itext = text;
+      etl::to_string(itext, ss.text, ss.spec, true);
+      return ss;
+    }
+
+    //*********************************
+    template <typename T>
+    friend string_stream& operator <<(string_stream& ss, const T& value)
+    {
+      etl::to_string(value, ss.text, ss.spec, true);
+      return ss;
+    }
+
+  private:
+
+    etl::istring&    text;
+    etl::format_spec spec;
+  };
+}
+
+#endif
diff --git a/include/etl/to_string.h b/include/etl/to_string.h
index 7ee633e9..b1cb280f 100644
--- a/include/etl/to_string.h
+++ b/include/etl/to_string.h
@@ -45,7 +45,8 @@ namespace etl
   /// Default format spec.
   //***************************************************************************
   template <typename T>
-  const etl::istring& to_string(const T value, etl::istring& str, const bool append = false)
+  typename etl::enable_if<!etl::is_same<T, etl::istring>::value && !etl::is_same<T, etl::string_view>::value, const etl::istring&>::type
+    to_string(const T value, etl::istring& str, bool append = false)
   {
     etl::format_spec format;
 
@@ -56,10 +57,63 @@ namespace etl
   /// Supplied format spec..
   //***************************************************************************
   template <typename T>
-  const etl::istring& to_string(const T value, etl::istring& str, const etl::format_spec& format, const bool append = false)
+  typename etl::enable_if<!etl::is_same<T, etl::istring>::value && !etl::is_same<T, etl::string_view>::value, const etl::istring&>::type
+    to_string(const T value, etl::istring& str, const etl::format_spec& format, bool append = false)
   {
     return private_to_string::to_string(value, str, format, append);
   }
+
+  //***************************************************************************
+  /// Default format spec.
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::istring>::value, const etl::istring&>::type
+    to_string(const T& value, etl::istring& str, bool append = false)
+  {
+    etl::format_spec format;
+
+    private_to_string::add_string(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Supplied format spec..
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::istring>::value, const etl::istring&>::type
+    to_string(const etl::istring& value, T& str, const etl::format_spec& format, bool append = false)
+  {
+    private_to_string::add_string(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Default format spec.
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::string_view>::value, const etl::istring&>::type
+    to_string(T value, etl::istring& str, bool append = false)
+  {
+    etl::format_spec format;
+
+    private_to_string::add_string_view(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Supplied format spec..
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::string_view>::value, const etl::istring&>::type
+    to_string(T value, etl::istring& str, const etl::format_spec& format, bool append = false)
+  {
+    private_to_string::add_string_view(value, str, format, append);
+
+    return str;
+  }
 }
 
 #endif
diff --git a/include/etl/to_u16string.h b/include/etl/to_u16string.h
index b87eb7e4..40473e1b 100644
--- a/include/etl/to_u16string.h
+++ b/include/etl/to_u16string.h
@@ -45,7 +45,8 @@ namespace etl
   /// Default format spec.
   //***************************************************************************
   template <typename T>
-  const etl::iu16string& to_string(const T value, etl::iu16string& str, const bool append = false)
+  typename etl::enable_if<!etl::is_same<T, etl::iu16string>::value && !etl::is_same<T, etl::u16string_view>::value, const etl::iu16string&>::type
+    to_string(const T value, etl::iu16string& str, bool append = false)
   {
     etl::u16format_spec format;
 
@@ -53,13 +54,66 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec.
+  /// Supplied format spec..
   //***************************************************************************
   template <typename T>
-  const etl::iu16string& to_string(const T value, etl::iu16string& str, const etl::u16format_spec& format, const bool append = false)
+  typename etl::enable_if<!etl::is_same<T, etl::iu16string>::value && !etl::is_same<T, etl::u16string_view>::value, const etl::iu16string&>::type
+    to_string(const T value, etl::iu16string& str, const etl::u16format_spec& format, bool append = false)
   {
     return private_to_string::to_string(value, str, format, append);
   }
+
+  //***************************************************************************
+  /// Default format spec.
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::iu16string>::value, const etl::iu16string&>::type
+    to_string(const T& value, etl::iu16string& str, bool append = false)
+  {
+    etl::u16format_spec format;
+
+    private_to_string::add_string(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Supplied format spec..
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::iu16string>::value, const etl::iu16string&>::type
+    to_string(const etl::iu16string& value, T& str, const etl::u16format_spec& format, bool append = false)
+  {
+    private_to_string::add_string(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Default format spec.
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::u16string_view>::value, const etl::iu16string&>::type
+    to_string(T value, etl::iu16string& str, bool append = false)
+  {
+    etl::u16format_spec format;
+
+    private_to_string::add_string_view(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Supplied format spec..
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::u16string_view>::value, const etl::iu16string&>::type
+    to_string(T value, etl::iu16string& str, const etl::u16format_spec& format, bool append = false)
+  {
+    private_to_string::add_string_view(value, str, format, append);
+
+    return str;
+  }
 }
 
 #endif
diff --git a/include/etl/to_u32string.h b/include/etl/to_u32string.h
index 88b7e3cf..36a7d805 100644
--- a/include/etl/to_u32string.h
+++ b/include/etl/to_u32string.h
@@ -45,7 +45,8 @@ namespace etl
   /// Default format spec.
   //***************************************************************************
   template <typename T>
-  const etl::iu32string& to_string(const T value, etl::iu32string& str, const bool append = false)
+  typename etl::enable_if<!etl::is_same<T, etl::iu32string>::value && !etl::is_same<T, etl::u32string_view>::value, const etl::iu32string&>::type
+    to_string(const T value, etl::iu32string& str, bool append = false)
   {
     etl::u32format_spec format;
 
@@ -53,13 +54,66 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec.
+  /// Supplied format spec..
   //***************************************************************************
   template <typename T>
-  const etl::iu32string& to_string(const T value, etl::iu32string& str, const etl::u32format_spec& format, const bool append = false)
+  typename etl::enable_if<!etl::is_same<T, etl::iu32string>::value && !etl::is_same<T, etl::u32string_view>::value, const etl::iu32string&>::type
+    to_string(const T value, etl::iu32string& str, const etl::u32format_spec& format, bool append = false)
   {
     return private_to_string::to_string(value, str, format, append);
   }
+
+  //***************************************************************************
+  /// Default format spec.
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::iu32string>::value, const etl::iu32string&>::type
+    to_string(const T& value, etl::iu32string& str, bool append = false)
+  {
+    etl::u32format_spec format;
+
+    private_to_string::add_string(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Supplied format spec..
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::iu32string>::value, const etl::iu32string&>::type
+    to_string(const etl::iu32string& value, T& str, const etl::u32format_spec& format, bool append = false)
+  {
+    private_to_string::add_string(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Default format spec.
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::u32string_view>::value, const etl::iu32string&>::type
+    to_string(T value, etl::iu32string& str, bool append = false)
+  {
+    etl::u32format_spec format;
+
+    private_to_string::add_string_view(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Supplied format spec..
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::u32string_view>::value, const etl::iu32string&>::type
+    to_string(T value, etl::iu32string& str, const etl::u32format_spec& format, bool append = false)
+  {
+    private_to_string::add_string_view(value, str, format, append);
+
+    return str;
+  }
 }
 
 #endif
diff --git a/include/etl/to_wstring.h b/include/etl/to_wstring.h
index fcbe728a..4ce8e813 100644
--- a/include/etl/to_wstring.h
+++ b/include/etl/to_wstring.h
@@ -45,7 +45,8 @@ namespace etl
   /// Default format spec.
   //***************************************************************************
   template <typename T>
-  const etl::iwstring& to_string(const T value, etl::iwstring& str, const bool append = false)
+  typename etl::enable_if<!etl::is_same<T, etl::iwstring>::value && !etl::is_same<T, etl::wstring_view>::value, const etl::iwstring&>::type
+    to_string(const T value, etl::iwstring& str, bool append = false)
   {
     etl::wformat_spec format;
 
@@ -53,13 +54,66 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec.
+  /// Supplied format spec..
   //***************************************************************************
   template <typename T>
-  const etl::iwstring& to_string(const T value, etl::iwstring& str, const etl::wformat_spec& format, const bool append = false)
+  typename etl::enable_if<!etl::is_same<T, etl::iwstring>::value && !etl::is_same<T, etl::wstring_view>::value, const etl::iwstring&>::type
+    to_string(const T value, etl::iwstring& str, const etl::wformat_spec& format, bool append = false)
   {
     return private_to_string::to_string(value, str, format, append);
   }
+
+  //***************************************************************************
+  /// Default format spec.
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::iwstring>::value, const etl::iwstring&>::type
+    to_string(const T& value, etl::iwstring& str, bool append = false)
+  {
+    etl::wformat_spec format;
+
+    private_to_string::add_string(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Supplied format spec..
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::iwstring>::value, const etl::iwstring&>::type
+    to_string(const etl::iwstring& value, T& str, const etl::wformat_spec& format, bool append = false)
+  {
+    private_to_string::add_string(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Default format spec.
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::wstring_view>::value, const etl::iwstring&>::type
+    to_string(T value, etl::iwstring& str, bool append = false)
+  {
+    etl::wformat_spec format;
+
+    private_to_string::add_string_view(value, str, format, append);
+
+    return str;
+  }
+
+  //***************************************************************************
+  /// Supplied format spec..
+  //***************************************************************************
+  template <typename T>
+  typename etl::enable_if<etl::is_same<T, etl::wstring_view>::value, const etl::iwstring&>::type
+    to_string(T value, etl::iwstring& str, const etl::wformat_spec& format, bool append = false)
+  {
+    private_to_string::add_string_view(value, str, format, append);
+
+    return str;
+  }
 }
 
 #endif
diff --git a/include/etl/u16string_stream.h b/include/etl/u16string_stream.h
new file mode 100644
index 00000000..f6251ee3
--- /dev/null
+++ b/include/etl/u16string_stream.h
@@ -0,0 +1,180 @@
+///\file
+
+/******************************************************************************
+The MIT License(MIT)
+
+Embedded Template Library.
+https://github.com/ETLCPP/etl
+https://www.etlcpp.com
+
+Copyright(c) 2020 jwellbelove
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files(the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions :
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+******************************************************************************/
+
+#ifndef ETL_U16STRING_STREAM_INCLUDED
+#define ETL_U16STRING_STREAM_INCLUDED
+
+///\ingroup string
+
+#include "platform.h"
+#include "u16string.h"
+#include "u16format_spec.h"
+#include "to_u16string.h"
+#include "string_view.h"
+
+namespace etl
+{
+  class u16string_stream
+  {
+  public:
+
+    typedef etl::u16format_spec         format_spec_type;
+    typedef etl::iu16string             istring_type;
+    typedef etl::iu16string::value_type value_type;
+
+    //*************************************************************************
+    /// Construct from text.
+    //*************************************************************************
+    explicit u16string_stream(etl::iu16string& text_)
+      : text(text_)
+    {
+    }
+
+    //*************************************************************************
+    /// Construct from text and format spec.
+    //*************************************************************************
+    u16string_stream(etl::iu16string& text_, etl::u16format_spec spec_)
+      : text(text_)
+      , spec(spec_)
+    {
+    }
+
+    //*************************************************************************
+    /// Set the format spec.
+    //*************************************************************************
+    void set_format(etl::u16format_spec spec_)
+    {
+      spec = spec_;
+    }
+
+    //*************************************************************************
+    /// Get a const reference to the format spec.
+    //*************************************************************************
+    const etl::u16format_spec& get_format() const
+    {
+      return spec;
+    }
+
+    //*************************************************************************
+    /// Get a reference to the current string.
+    //*************************************************************************
+    etl::iu16string& str()
+    {
+      return text;
+    }
+
+    //*************************************************************************
+    /// Get a const reference to the current string.
+    //*************************************************************************
+    const etl::iu16string& str() const
+    {
+      return text;
+    }
+
+    //*************************************************************************
+    /// Resets the stream to the supplied string.
+    //*************************************************************************
+    void str(const etl::iu16string::value_type* p)
+    {
+      text.assign(p);
+    }
+
+    //*************************************************************************
+    /// Resets the stream to the supplied string.
+    //*************************************************************************
+    void str(const etl::iu16string& is)
+    {
+      text.assign(is);
+    }
+
+    //*************************************************************************
+    /// Get the current size of the string.
+    //*************************************************************************
+    size_t size() const
+    {
+      return text.size();
+    }
+
+    //*************************************************************************
+    /// Stream operators.
+    //*************************************************************************
+    friend u16string_stream& operator <<(u16string_stream& ss, etl::u16format_spec spec)
+    {
+      ss.spec = spec;
+      return ss;
+    }
+
+    //*********************************
+    friend u16string_stream& operator <<(u16string_stream& ss, etl::u16string_view view)
+    {
+      etl::to_string(view, ss.text, ss.spec, true);
+      return ss;
+    }
+
+    //*********************************
+    friend u16string_stream& operator <<(u16string_stream& ss, etl::iu16string::const_pointer p)
+    {
+      etl::u16string_view view(p);
+      ss << view;
+      return ss;
+    } 
+
+    //*********************************
+    friend u16string_stream& operator <<(u16string_stream& ss, const etl::iu16string& text)
+    {
+      etl::to_string(text, ss.text, ss.spec, true);
+      return ss;
+    }
+
+    //*********************************
+    template <size_t SIZE>
+    friend u16string_stream& operator <<(u16string_stream& ss, const etl::u16string<SIZE>& text)
+    {
+      const etl::iu16string& itext = text;
+      etl::to_string(itext, ss.text, ss.spec, true);
+      return ss;
+    }
+
+    //*********************************
+    template <typename T>
+    friend u16string_stream& operator <<(u16string_stream& ss, const T& value)
+    {
+      etl::to_string(value, ss.text, ss.spec, true);
+      return ss;
+    }
+
+  private:
+
+    etl::iu16string&    text;
+    etl::u16format_spec spec;
+  };
+}
+
+#endif
diff --git a/include/etl/u32string_stream.h b/include/etl/u32string_stream.h
new file mode 100644
index 00000000..94044744
--- /dev/null
+++ b/include/etl/u32string_stream.h
@@ -0,0 +1,180 @@
+///\file
+
+/******************************************************************************
+The MIT License(MIT)
+
+Embedded Template Library.
+https://github.com/ETLCPP/etl
+https://www.etlcpp.com
+
+Copyright(c) 2020 jwellbelove
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files(the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions :
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+******************************************************************************/
+
+#ifndef ETL_U32STRING_STREAM_INCLUDED
+#define ETL_U32STRING_STREAM_INCLUDED
+
+///\ingroup string
+
+#include "platform.h"
+#include "u32string.h"
+#include "u32format_spec.h"
+#include "to_u32string.h"
+#include "string_view.h"
+
+namespace etl
+{
+  class u32string_stream
+  {
+  public:
+
+    typedef etl::u32format_spec         format_spec_type;
+    typedef etl::iu32string             istring_type;
+    typedef etl::iu32string::value_type value_type;
+
+    //*************************************************************************
+    /// Construct from text.
+    //*************************************************************************
+    explicit u32string_stream(etl::iu32string& text_)
+      : text(text_)
+    {
+    }
+
+    //*************************************************************************
+    /// Construct from text and format spec.
+    //*************************************************************************
+    u32string_stream(etl::iu32string& text_, etl::u32format_spec spec_)
+      : text(text_)
+      , spec(spec_)
+    {
+    }
+
+    //*************************************************************************
+    /// Set the format spec.
+    //*************************************************************************
+    void set_format(etl::u32format_spec spec_)
+    {
+      spec = spec_;
+    }
+
+    //*************************************************************************
+    /// Get a const reference to the format spec.
+    //*************************************************************************
+    const etl::u32format_spec& get_format() const
+    {
+      return spec;
+    }
+
+    //*************************************************************************
+    /// Get a reference to the current string.
+    //*************************************************************************
+    etl::iu32string& str()
+    {
+      return text;
+    }
+
+    //*************************************************************************
+    /// Get a const reference to the current string.
+    //*************************************************************************
+    const etl::iu32string& str() const
+    {
+      return text;
+    }
+
+    //*************************************************************************
+    /// Resets the stream to the supplied string.
+    //*************************************************************************
+    void str(const etl::iu32string::value_type* p)
+    {
+      text.assign(p);
+    }
+
+    //*************************************************************************
+    /// Resets the stream to the supplied string.
+    //*************************************************************************
+    void str(const etl::iu32string& is)
+    {
+      text.assign(is);
+    }
+
+    //*************************************************************************
+    /// Get the current size of the string.
+    //*************************************************************************
+    size_t size() const
+    {
+      return text.size();
+    }
+
+    //*************************************************************************
+    /// Stream operators.
+    //*************************************************************************
+    friend u32string_stream& operator <<(u32string_stream& ss, etl::u32format_spec spec)
+    {
+      ss.spec = spec;
+      return ss;
+    }
+
+    //*********************************
+    friend u32string_stream& operator <<(u32string_stream& ss, etl::u32string_view view)
+    {
+      etl::to_string(view, ss.text, ss.spec, true);
+      return ss;
+    }
+
+    //*********************************
+    friend u32string_stream& operator <<(u32string_stream& ss, etl::iu32string::const_pointer p)
+    {
+      etl::u32string_view view(p);
+      ss << view;
+      return ss;
+    }
+
+    //*********************************
+    friend u32string_stream& operator <<(u32string_stream& ss, const etl::iu32string& text)
+    {
+      etl::to_string(text, ss.text, ss.spec, true);
+      return ss;
+    }
+
+    //*********************************
+    template <size_t SIZE>
+    friend u32string_stream& operator <<(u32string_stream& ss, const etl::u32string<SIZE>& text)
+    {
+      const etl::iu32string& itext = text;
+      etl::to_string(itext, ss.text, ss.spec, true);
+      return ss;
+    }
+
+    //*********************************
+    template <typename T>
+    friend u32string_stream& operator <<(u32string_stream& ss, const T& value)
+    {
+      etl::to_string(value, ss.text, ss.spec, true);
+      return ss;
+    }
+
+  private:
+
+    etl::iu32string&    text;
+    etl::u32format_spec spec;
+  };
+}
+
+#endif
diff --git a/include/etl/wstring_stream.h b/include/etl/wstring_stream.h
new file mode 100644
index 00000000..9c786da6
--- /dev/null
+++ b/include/etl/wstring_stream.h
@@ -0,0 +1,180 @@
+///\file
+
+/******************************************************************************
+The MIT License(MIT)
+
+Embedded Template Library.
+https://github.com/ETLCPP/etl
+https://www.etlcpp.com
+
+Copyright(c) 2020 jwellbelove
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files(the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions :
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+******************************************************************************/
+
+#ifndef ETL_WSTRING_STREAM_INCLUDED
+#define ETL_WSTRING_STREAM_INCLUDED
+
+///\ingroup string
+
+#include "platform.h"
+#include "cstring.h"
+#include "wformat_spec.h"
+#include "to_wstring.h"
+#include "string_view.h"
+
+namespace etl
+{
+  class wstring_stream
+  {
+  public:
+
+    typedef etl::wformat_spec         format_spec_type;
+    typedef etl::iwstring             istring_type;
+    typedef etl::iwstring::value_type value_type;
+
+    //*************************************************************************
+    /// Construct from text.
+    //*************************************************************************
+    explicit wstring_stream(etl::iwstring& text_)
+      : text(text_)
+    {
+    }
+
+    //*************************************************************************
+    /// Construct from text and format spec.
+    //*************************************************************************
+    wstring_stream(etl::iwstring& text_, etl::wformat_spec spec_)
+      : text(text_)
+      , spec(spec_)
+    {
+    }
+
+    //*************************************************************************
+    /// Set the format spec.
+    //*************************************************************************
+    void set_format(etl::wformat_spec spec_)
+    {
+      spec = spec_;
+    }
+
+    //*************************************************************************
+    /// Get a const reference to the format spec.
+    //*************************************************************************
+    const etl::wformat_spec& get_format() const
+    {
+      return spec;
+    }
+
+    //*************************************************************************
+    /// Get a reference to the current string.
+    //*************************************************************************
+    etl::iwstring& str()
+    {
+      return text;
+    }
+
+    //*************************************************************************
+    /// Get a const reference to the current string.
+    //*************************************************************************
+    const etl::iwstring& str() const
+    {
+      return text;
+    }
+
+    //*************************************************************************
+    /// Resets the stream to the supplied string.
+    //*************************************************************************
+    void str(const etl::iwstring::value_type* p)
+    {
+      text.assign(p);
+    }
+
+    //*************************************************************************
+    /// Resets the stream to the supplied string.
+    //*************************************************************************
+    void str(const etl::iwstring& is)
+    {
+      text.assign(is);
+    }
+
+    //*************************************************************************
+    /// Get the current size of the string.
+    //*************************************************************************
+    size_t size() const
+    {
+      return text.size();
+    }
+
+    //*************************************************************************
+    /// Stream operators.
+    //*************************************************************************
+    friend wstring_stream& operator <<(wstring_stream& ss, etl::wformat_spec spec)
+    {
+      ss.spec = spec;
+      return ss;
+    }
+
+    //*********************************
+    friend wstring_stream& operator <<(wstring_stream& ss, etl::wstring_view view)
+    {
+      etl::to_string(view, ss.text, ss.spec, true);
+      return ss;
+    }
+    
+    //*********************************
+    friend wstring_stream& operator <<(wstring_stream& ss, etl::iwstring::const_pointer p)
+    {
+      etl::wstring_view view(p);
+      ss << view;
+      return ss;
+    }
+
+    //*********************************
+    friend wstring_stream& operator <<(wstring_stream& ss, const etl::iwstring& text)
+    {
+      etl::to_string(text, ss.text, ss.spec, true);
+      return ss;
+    }
+
+    //*********************************
+    template <size_t SIZE>
+    friend wstring_stream& operator <<(wstring_stream& ss, const etl::wstring<SIZE>& text)
+    {
+      const etl::iwstring& itext = text;
+      etl::to_string(itext, ss.text, ss.spec, true);
+      return ss;
+    }
+
+    //*********************************
+    template <typename T>
+    friend wstring_stream& operator <<(wstring_stream& ss, const T& value)
+    {
+      etl::to_string(value, ss.text, ss.spec, true);
+      return ss;
+    }
+
+  private:
+
+    etl::iwstring&    text;
+    etl::wformat_spec spec;
+  };
+}
+
+#endif
diff --git a/test/test_string_stream.cpp b/test/test_string_stream.cpp
new file mode 100644
index 00000000..82b06836
--- /dev/null
+++ b/test/test_string_stream.cpp
@@ -0,0 +1,220 @@
+/******************************************************************************
+The MIT License(MIT)
+
+Embedded Template Library.
+https://github.com/ETLCPP/etl
+https://www.etlcpp.com
+
+Copyright(c) 2020 jwellbelove
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files(the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions :
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+******************************************************************************/
+
+#include "UnitTest++/UnitTest++.h"
+
+#include <ostream>
+#include <sstream>
+#include <iomanip>
+
+#include "etl/string_stream.h"
+#include "etl/cstring.h"
+#include "etl/format_spec.h"
+
+#undef STR
+#define STR(x) x
+
+namespace
+{
+  using String  = etl::string<50>;
+  using IString = etl::istring;
+  using Stream  = etl::string_stream;
+  using Format  = etl::format_spec;
+
+  //***********************************
+  struct Custom
+  {
+    int x;
+    int y;
+  };
+
+  //***********************************
+  Stream& operator <<(Stream& ss, const Custom& value)
+  {
+    ss << STR("X = ") << value.x << STR(" : Y = ") << value.y;
+    return ss;
+  }
+
+  //***********************************
+  std::ostream& operator << (std::ostream& os, const IString& str)
+  {
+    for (auto c : str)
+    {
+      os << c;
+    }
+
+    return os;
+  }
+
+  SUITE(test_string_stream)
+  {
+    //*************************************************************************
+    TEST(test_default_format)
+    {
+      String str;
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << hello << STR(" World ") << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("Hello World 123")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_format)
+    {
+      String str;
+      Format format = Format().base(10).width(10).fill(STR('#'));
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << format << hello << STR("World") << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("#####Hello#####World#######123")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_multi_format)
+    {
+      String str;
+      Format format1 = Format().base(10).width(10).fill(STR('#'));
+      Format format2 = Format().base(10).width(8).fill(STR('*')).left();
+      Format format3 = Format().base(16).width(4).fill(STR(' ')).right();
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << format1 << hello << format2 << STR("World") << format3 << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("#####HelloWorld***  7B")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_class_default_format)
+    {
+      String str;
+
+      Stream ss(str);
+
+      String value_str(STR("Value: "));
+      IString& ivalue_str = value_str;
+      Custom value = { 1, 2 };
+
+      ss << ivalue_str << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("Value: X = 1 : Y = 2")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_get_format)
+    {
+      String str;
+      Format format = Format().base(16).width(4).fill(STR(' ')).right();
+
+      Stream ss(str, format);
+
+      Format format2 = ss.get_format();
+
+      CHECK(format == format2);
+    }
+
+    //*************************************************************************
+    TEST(test_set_from_character_pointer)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(STR("Hello"));
+
+      CHECK_EQUAL(String(STR("Hello")), ss.str());
+    }
+
+    //*************************************************************************
+    TEST(test_set_from_string)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      CHECK_EQUAL(String(STR("Hello")), ss.str());
+    }
+
+    //*************************************************************************
+    TEST(test_get_istring)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      IString& istr = ss.str();
+      istr.resize(istr.size() - 1);
+
+      CHECK_EQUAL(String(STR("Hell")), istr);
+    }
+
+    //*************************************************************************
+    TEST(test_get_const_istring)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      const IString& istr = ss.str();
+
+      CHECK_EQUAL(String(STR("Hello")), istr);
+    }
+
+    //*************************************************************************
+    TEST(test_get_size)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      CHECK_EQUAL(str.size(), ss.size());
+    }
+  };
+}
+
diff --git a/test/test_u16string_stream.cpp b/test/test_u16string_stream.cpp
new file mode 100644
index 00000000..9bfa9cfd
--- /dev/null
+++ b/test/test_u16string_stream.cpp
@@ -0,0 +1,220 @@
+/******************************************************************************
+The MIT License(MIT)
+
+Embedded Template Library.
+https://github.com/ETLCPP/etl
+https://www.etlcpp.com
+
+Copyright(c) 2020 jwellbelove
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files(the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions :
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+******************************************************************************/
+
+#include "UnitTest++/UnitTest++.h"
+
+#include <ostream>
+#include <sstream>
+#include <iomanip>
+
+#include "etl/u16string_stream.h"
+#include "etl/u16string.h"
+#include "etl/format_spec.h"
+
+#undef STR
+#define STR(x) u##x
+
+namespace
+{
+  using String  = etl::u16string<50>;
+  using IString = etl::iu16string;
+  using Stream  = etl::u16string_stream;
+  using Format  = etl::u16format_spec;
+
+  //***********************************
+  struct Custom
+  {
+    int x;
+    int y;
+  };
+
+  //***********************************
+  Stream& operator <<(Stream& ss, const Custom& value)
+  {
+    ss << STR("X = ") << value.x << STR(" : Y = ") << value.y;
+    return ss;
+  }
+
+  //***********************************
+  std::ostream& operator << (std::ostream& os, const IString& str)
+  {
+    for (auto c : str)
+    {
+      os << c;
+    }
+
+    return os;
+  }
+
+  SUITE(test_string_stream)
+  {
+    //*************************************************************************
+    TEST(test_default_format)
+    {
+      String str;
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << hello << STR(" World ") << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("Hello World 123")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_format)
+    {
+      String str;
+      Format format = Format().base(10).width(10).fill(STR('#'));
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << format << hello << STR("World") << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("#####Hello#####World#######123")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_multi_format)
+    {
+      String str;
+      Format format1 = Format().base(10).width(10).fill(STR('#'));
+      Format format2 = Format().base(10).width(8).fill(STR('*')).left();
+      Format format3 = Format().base(16).width(4).fill(STR(' ')).right();
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << format1 << hello << format2 << STR("World") << format3 << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("#####HelloWorld***  7B")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_class_default_format)
+    {
+      String str;
+
+      Stream ss(str);
+
+      String value_str(STR("Value: "));
+      IString& ivalue_str = value_str;
+      Custom value = { 1, 2 };
+
+      ss << ivalue_str << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("Value: X = 1 : Y = 2")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_get_format)
+    {
+      String str;
+      Format format = Format().base(16).width(4).fill(STR(' ')).right();
+
+      Stream ss(str, format);
+
+      Format format2 = ss.get_format();
+
+      CHECK(format == format2);
+    }
+
+    //*************************************************************************
+    TEST(test_set_from_character_pointer)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(STR("Hello"));
+
+      CHECK_EQUAL(String(STR("Hello")), ss.str());
+    }
+
+    //*************************************************************************
+    TEST(test_set_from_string)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      CHECK_EQUAL(String(STR("Hello")), ss.str());
+    }
+
+    //*************************************************************************
+    TEST(test_get_istring)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      IString& istr = ss.str();
+      istr.resize(istr.size() - 1);
+
+      CHECK_EQUAL(String(STR("Hell")), istr);
+    }
+
+    //*************************************************************************
+    TEST(test_get_const_istring)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      const IString& istr = ss.str();
+
+      CHECK_EQUAL(String(STR("Hello")), istr);
+    }
+
+    //*************************************************************************
+    TEST(test_get_size)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      CHECK_EQUAL(str.size(), ss.size());
+    }
+  };
+}
+
diff --git a/test/test_u32string_stream.cpp b/test/test_u32string_stream.cpp
new file mode 100644
index 00000000..84f00031
--- /dev/null
+++ b/test/test_u32string_stream.cpp
@@ -0,0 +1,220 @@
+/******************************************************************************
+The MIT License(MIT)
+
+Embedded Template Library.
+https://github.com/ETLCPP/etl
+https://www.etlcpp.com
+
+Copyright(c) 2020 jwellbelove
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files(the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions :
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+******************************************************************************/
+
+#include "UnitTest++/UnitTest++.h"
+
+#include <ostream>
+#include <sstream>
+#include <iomanip>
+
+#include "etl/u32string_stream.h"
+#include "etl/u32string.h"
+#include "etl/format_spec.h"
+
+#undef STR
+#define STR(x) U##x
+
+namespace
+{
+  using String  = etl::u32string<50>;
+  using IString = etl::iu32string;
+  using Stream  = etl::u32string_stream;
+  using Format  = etl::u32format_spec;
+
+  //***********************************
+  struct Custom
+  {
+    int x;
+    int y;
+  };
+
+  //***********************************
+  Stream& operator <<(Stream& ss, const Custom& value)
+  {
+    ss << STR("X = ") << value.x << STR(" : Y = ") << value.y;
+    return ss;
+  }
+
+  //***********************************
+  std::ostream& operator << (std::ostream& os, const IString& str)
+  {
+    for (auto c : str)
+    {
+      os << c;
+    }
+
+    return os;
+  }
+
+  SUITE(test_string_stream)
+  {
+    //*************************************************************************
+    TEST(test_default_format)
+    {
+      String str;
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << hello << STR(" World ") << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("Hello World 123")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_format)
+    {
+      String str;
+      Format format = Format().base(10).width(10).fill(STR('#'));
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << format << hello << STR("World") << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("#####Hello#####World#######123")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_multi_format)
+    {
+      String str;
+      Format format1 = Format().base(10).width(10).fill(STR('#'));
+      Format format2 = Format().base(10).width(8).fill(STR('*')).left();
+      Format format3 = Format().base(16).width(4).fill(STR(' ')).right();
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << format1 << hello << format2 << STR("World") << format3 << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("#####HelloWorld***  7B")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_class_default_format)
+    {
+      String str;
+
+      Stream ss(str);
+
+      String value_str(STR("Value: "));
+      IString& ivalue_str = value_str;
+      Custom value = { 1, 2 };
+
+      ss << ivalue_str << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("Value: X = 1 : Y = 2")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_get_format)
+    {
+      String str;
+      Format format = Format().base(16).width(4).fill(STR(' ')).right();
+
+      Stream ss(str, format);
+
+      Format format2 = ss.get_format();
+
+      CHECK(format == format2);
+    }
+
+    //*************************************************************************
+    TEST(test_set_from_character_pointer)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(STR("Hello"));
+
+      CHECK_EQUAL(String(STR("Hello")), ss.str());
+    }
+
+    //*************************************************************************
+    TEST(test_set_from_string)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      CHECK_EQUAL(String(STR("Hello")), ss.str());
+    }
+
+    //*************************************************************************
+    TEST(test_get_istring)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      IString& istr = ss.str();
+      istr.resize(istr.size() - 1);
+
+      CHECK_EQUAL(String(STR("Hell")), istr);
+    }
+
+    //*************************************************************************
+    TEST(test_get_const_istring)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      const IString& istr = ss.str();
+
+      CHECK_EQUAL(String(STR("Hello")), istr);
+    }
+
+    //*************************************************************************
+    TEST(test_get_size)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      CHECK_EQUAL(str.size(), ss.size());
+    }
+  };
+}
+
diff --git a/test/test_wstring_stream.cpp b/test/test_wstring_stream.cpp
new file mode 100644
index 00000000..09a72053
--- /dev/null
+++ b/test/test_wstring_stream.cpp
@@ -0,0 +1,220 @@
+/******************************************************************************
+The MIT License(MIT)
+
+Embedded Template Library.
+https://github.com/ETLCPP/etl
+https://www.etlcpp.com
+
+Copyright(c) 2020 jwellbelove
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files(the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions :
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+******************************************************************************/
+
+#include "UnitTest++/UnitTest++.h"
+
+#include <ostream>
+#include <sstream>
+#include <iomanip>
+
+#include "etl/wstring_stream.h"
+#include "etl/wstring.h"
+#include "etl/format_spec.h"
+
+#undef STR
+#define STR(x) L##x
+
+namespace
+{
+  using String  = etl::wstring<50>;
+  using IString = etl::iwstring;
+  using Stream  = etl::wstring_stream;
+  using Format  = etl::wformat_spec;
+
+  //***********************************
+  struct Custom
+  {
+    int x;
+    int y;
+  };
+
+  //***********************************
+  Stream& operator <<(Stream& ss, const Custom& value)
+  {
+    ss << STR("X = ") << value.x << STR(" : Y = ") << value.y;
+    return ss;
+  }
+
+  //***********************************
+  std::ostream& operator << (std::ostream& os, const IString& str)
+  {
+    for (auto c : str)
+    {
+      os << c;
+    }
+
+    return os;
+  }
+
+  SUITE(test_string_stream)
+  {
+    //*************************************************************************
+    TEST(test_default_format)
+    {
+      String str;
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << hello << STR(" World ") << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("Hello World 123")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_format)
+    {
+      String str;
+      Format format = Format().base(10).width(10).fill(STR('#'));
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << format << hello << STR("World") << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("#####Hello#####World#######123")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_multi_format)
+    {
+      String str;
+      Format format1 = Format().base(10).width(10).fill(STR('#'));
+      Format format2 = Format().base(10).width(8).fill(STR('*')).left();
+      Format format3 = Format().base(16).width(4).fill(STR(' ')).right();
+
+      Stream ss(str);
+
+      int value = 123;
+      String hello(STR("Hello"));
+      ss << format1 << hello << format2 << STR("World") << format3 << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("#####HelloWorld***  7B")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_custom_class_default_format)
+    {
+      String str;
+
+      Stream ss(str);
+
+      String value_str(STR("Value: "));
+      IString& ivalue_str = value_str;
+      Custom value = { 1, 2 };
+
+      ss << ivalue_str << value;
+
+      String result = ss.str();
+
+      CHECK_EQUAL(String(STR("Value: X = 1 : Y = 2")), result);
+    }
+
+    //*************************************************************************
+    TEST(test_get_format)
+    {
+      String str;
+      Format format = Format().base(16).width(4).fill(STR(' ')).right();
+
+      Stream ss(str, format);
+
+      Format format2 = ss.get_format();
+
+      CHECK(format == format2);
+    }
+
+    //*************************************************************************
+    TEST(test_set_from_character_pointer)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(STR("Hello"));
+
+      CHECK_EQUAL(String(STR("Hello")), ss.str());
+    }
+
+    //*************************************************************************
+    TEST(test_set_from_string)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      CHECK_EQUAL(String(STR("Hello")), ss.str());
+    }
+
+    //*************************************************************************
+    TEST(test_get_istring)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      IString& istr = ss.str();
+      istr.resize(istr.size() - 1);
+
+      CHECK_EQUAL(String(STR("Hell")), istr);
+    }
+
+    //*************************************************************************
+    TEST(test_get_const_istring)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      const IString& istr = ss.str();
+
+      CHECK_EQUAL(String(STR("Hello")), istr);
+    }
+
+    //*************************************************************************
+    TEST(test_get_size)
+    {
+      String str;
+      Stream ss(str);
+
+      ss.str(String(STR("Hello")));
+
+      CHECK_EQUAL(str.size(), ss.size());
+    }
+  };
+}
+
diff --git a/test/vs2019/etl.vcxproj b/test/vs2019/etl.vcxproj
index f980b3da..acd09ab1 100644
--- a/test/vs2019/etl.vcxproj
+++ b/test/vs2019/etl.vcxproj
@@ -1121,6 +1121,7 @@
     <ClInclude Include="..\..\include\etl\queue_spsc_isr.h" />
     <ClInclude Include="..\..\include\etl\queue_mpmc_mutex.h" />
     <ClInclude Include="..\..\include\etl\sqrt.h" />
+    <ClInclude Include="..\..\include\etl\string_stream.h" />
     <ClInclude Include="..\..\include\etl\string_view.h" />
     <ClInclude Include="..\..\include\etl\task.h" />
     <ClInclude Include="..\..\include\etl\timer.h" />
@@ -1131,7 +1132,9 @@
     <ClInclude Include="..\..\include\etl\type_lookup.h" />
     <ClInclude Include="..\..\include\etl\type_select.h" />
     <ClInclude Include="..\..\include\etl\u16format_spec.h" />
+    <ClInclude Include="..\..\include\etl\u16string_stream.h" />
     <ClInclude Include="..\..\include\etl\u32format_spec.h" />
+    <ClInclude Include="..\..\include\etl\u32string_stream.h" />
     <ClInclude Include="..\..\include\etl\variant_pool.h" />
     <ClInclude Include="..\..\include\etl\version.h" />
     <ClInclude Include="..\..\include\etl\algorithm.h" />
@@ -1228,6 +1231,7 @@
     <ClInclude Include="..\..\include\etl\visitor.h" />
     <ClInclude Include="..\..\include\etl\wformat_spec.h" />
     <ClInclude Include="..\..\include\etl\wstring.h" />
+    <ClInclude Include="..\..\include\etl\wstring_stream.h" />
     <ClInclude Include="..\data.h" />
     <ClInclude Include="..\etl_profile.h" />
     <ClInclude Include="..\murmurhash3.h" />
@@ -1618,6 +1622,7 @@
     <ClCompile Include="..\test_stack.cpp" />
     <ClCompile Include="..\test_string_char.cpp" />
     <ClCompile Include="..\test_string_char_external_buffer.cpp" />
+    <ClCompile Include="..\test_string_stream.cpp" />
     <ClCompile Include="..\test_string_u16.cpp" />
     <ClCompile Include="..\test_string_u16_external_buffer.cpp" />
     <ClCompile Include="..\test_string_u32.cpp" />
@@ -1634,6 +1639,8 @@
     <ClCompile Include="..\test_type_lookup.cpp" />
     <ClCompile Include="..\test_type_select.cpp" />
     <ClCompile Include="..\test_type_traits.cpp" />
+    <ClCompile Include="..\test_u16string_stream.cpp" />
+    <ClCompile Include="..\test_u32string_stream.cpp" />
     <ClCompile Include="..\test_unordered_map.cpp" />
     <ClCompile Include="..\test_unordered_multimap.cpp" />
     <ClCompile Include="..\test_unordered_multiset.cpp" />
@@ -1648,6 +1655,7 @@
     <ClCompile Include="..\test_vector_pointer.cpp" />
     <ClCompile Include="..\test_vector_pointer_external_buffer.cpp" />
     <ClCompile Include="..\test_visitor.cpp" />
+    <ClCompile Include="..\test_wstring_stream.cpp" />
     <ClCompile Include="..\test_xor_checksum.cpp" />
     <ClCompile Include="..\test_xor_rotate_checksum.cpp" />
   </ItemGroup>
diff --git a/test/vs2019/etl.vcxproj.filters b/test/vs2019/etl.vcxproj.filters
index c727bd0d..8e03bfcc 100644
--- a/test/vs2019/etl.vcxproj.filters
+++ b/test/vs2019/etl.vcxproj.filters
@@ -855,6 +855,18 @@
     <ClInclude Include="..\..\include\etl\parameter_pack.h">
       <Filter>ETL\Utilities</Filter>
     </ClInclude>
+    <ClInclude Include="..\..\include\etl\string_stream.h">
+      <Filter>ETL\Strings</Filter>
+    </ClInclude>
+    <ClInclude Include="..\..\include\etl\wstring_stream.h">
+      <Filter>ETL\Strings</Filter>
+    </ClInclude>
+    <ClInclude Include="..\..\include\etl\u16string_stream.h">
+      <Filter>ETL\Strings</Filter>
+    </ClInclude>
+    <ClInclude Include="..\..\include\etl\u32string_stream.h">
+      <Filter>ETL\Strings</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="..\main.cpp">
@@ -1331,6 +1343,18 @@
     <ClCompile Include="..\test_parameter_pack.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\test_string_stream.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="..\test_wstring_stream.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="..\test_u16string_stream.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="..\test_u32string_stream.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <None Include="..\..\library.properties">

From 3e2352770bffe3683cd7c894b95c70729c1e0976 Mon Sep 17 00:00:00 2001
From: John Wellbelove <github@wellbelove.co.uk>
Date: Sun, 5 Jul 2020 20:55:14 +0100
Subject: [PATCH 2/2] string streams

---
 include/etl/to_string.h    | 12 +++++++++---
 include/etl/to_u16string.h | 12 +++++++++---
 include/etl/to_u32string.h | 12 +++++++++---
 include/etl/to_wstring.h   | 12 +++++++++---
 include/etl/version.h      |  4 ++--
 library.json               |  2 +-
 library.properties         |  2 +-
 support/Release notes.txt  | 14 ++++++++++++++
 8 files changed, 54 insertions(+), 16 deletions(-)

diff --git a/include/etl/to_string.h b/include/etl/to_string.h
index b1cb280f..c8fe60b0 100644
--- a/include/etl/to_string.h
+++ b/include/etl/to_string.h
@@ -43,6 +43,7 @@ namespace etl
 {
   //***************************************************************************
   /// Default format spec.
+  /// !etl::istring && !etl::string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<!etl::is_same<T, etl::istring>::value && !etl::is_same<T, etl::string_view>::value, const etl::istring&>::type
@@ -54,7 +55,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// !etl::istring && !etl::string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<!etl::is_same<T, etl::istring>::value && !etl::is_same<T, etl::string_view>::value, const etl::istring&>::type
@@ -65,6 +67,7 @@ namespace etl
 
   //***************************************************************************
   /// Default format spec.
+  /// etl::istring
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::istring>::value, const etl::istring&>::type
@@ -78,7 +81,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// etl::istring
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::istring>::value, const etl::istring&>::type
@@ -91,6 +95,7 @@ namespace etl
 
   //***************************************************************************
   /// Default format spec.
+  /// etl::string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::string_view>::value, const etl::istring&>::type
@@ -104,7 +109,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// etl::string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::string_view>::value, const etl::istring&>::type
diff --git a/include/etl/to_u16string.h b/include/etl/to_u16string.h
index 40473e1b..cfb6ffe8 100644
--- a/include/etl/to_u16string.h
+++ b/include/etl/to_u16string.h
@@ -43,6 +43,7 @@ namespace etl
 {
   //***************************************************************************
   /// Default format spec.
+  /// !etl::iu16string && !etl::u16string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<!etl::is_same<T, etl::iu16string>::value && !etl::is_same<T, etl::u16string_view>::value, const etl::iu16string&>::type
@@ -54,7 +55,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// !etl::iu16string && !etl::u16string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<!etl::is_same<T, etl::iu16string>::value && !etl::is_same<T, etl::u16string_view>::value, const etl::iu16string&>::type
@@ -65,6 +67,7 @@ namespace etl
 
   //***************************************************************************
   /// Default format spec.
+  /// etl::iu16string
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::iu16string>::value, const etl::iu16string&>::type
@@ -78,7 +81,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// etl::iu16string
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::iu16string>::value, const etl::iu16string&>::type
@@ -91,6 +95,7 @@ namespace etl
 
   //***************************************************************************
   /// Default format spec.
+  /// etl::u16string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::u16string_view>::value, const etl::iu16string&>::type
@@ -104,7 +109,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// etl::u16string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::u16string_view>::value, const etl::iu16string&>::type
diff --git a/include/etl/to_u32string.h b/include/etl/to_u32string.h
index 36a7d805..f07451cd 100644
--- a/include/etl/to_u32string.h
+++ b/include/etl/to_u32string.h
@@ -43,6 +43,7 @@ namespace etl
 {
   //***************************************************************************
   /// Default format spec.
+  /// !etl::iu32string && !etl::u32string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<!etl::is_same<T, etl::iu32string>::value && !etl::is_same<T, etl::u32string_view>::value, const etl::iu32string&>::type
@@ -54,7 +55,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// !etl::iu32string && !etl::u32string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<!etl::is_same<T, etl::iu32string>::value && !etl::is_same<T, etl::u32string_view>::value, const etl::iu32string&>::type
@@ -65,6 +67,7 @@ namespace etl
 
   //***************************************************************************
   /// Default format spec.
+  /// etl::iu32string
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::iu32string>::value, const etl::iu32string&>::type
@@ -78,7 +81,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// etl::iu32string
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::iu32string>::value, const etl::iu32string&>::type
@@ -91,6 +95,7 @@ namespace etl
 
   //***************************************************************************
   /// Default format spec.
+  /// etl::u32string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::u32string_view>::value, const etl::iu32string&>::type
@@ -104,7 +109,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// etl::u32string_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::u32string_view>::value, const etl::iu32string&>::type
diff --git a/include/etl/to_wstring.h b/include/etl/to_wstring.h
index 4ce8e813..1612d02e 100644
--- a/include/etl/to_wstring.h
+++ b/include/etl/to_wstring.h
@@ -43,6 +43,7 @@ namespace etl
 {
   //***************************************************************************
   /// Default format spec.
+  /// !etl::iwstring && !etl::wstring_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<!etl::is_same<T, etl::iwstring>::value && !etl::is_same<T, etl::wstring_view>::value, const etl::iwstring&>::type
@@ -54,7 +55,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// !etl::iwstring && !etl::wstring_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<!etl::is_same<T, etl::iwstring>::value && !etl::is_same<T, etl::wstring_view>::value, const etl::iwstring&>::type
@@ -65,6 +67,7 @@ namespace etl
 
   //***************************************************************************
   /// Default format spec.
+  /// etl::iwstring
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::iwstring>::value, const etl::iwstring&>::type
@@ -78,7 +81,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// etl::iwstring
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::iwstring>::value, const etl::iwstring&>::type
@@ -91,6 +95,7 @@ namespace etl
 
   //***************************************************************************
   /// Default format spec.
+  /// etl::wstring_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::wstring_view>::value, const etl::iwstring&>::type
@@ -104,7 +109,8 @@ namespace etl
   }
 
   //***************************************************************************
-  /// Supplied format spec..
+  /// Supplied format spec.
+  /// etl::wstring_view
   //***************************************************************************
   template <typename T>
   typename etl::enable_if<etl::is_same<T, etl::wstring_view>::value, const etl::iwstring&>::type
diff --git a/include/etl/version.h b/include/etl/version.h
index 3ff851c4..81379974 100644
--- a/include/etl/version.h
+++ b/include/etl/version.h
@@ -38,8 +38,8 @@ SOFTWARE.
 ///\ingroup utilities
 
 #define ETL_VERSION_MAJOR 18
-#define ETL_VERSION_MINOR  3
-#define ETL_VERSION_PATCH  4
+#define ETL_VERSION_MINOR  5
+#define ETL_VERSION_PATCH  0
 #define ETL_VERSION       ETL_STRINGIFY(ETL_VERSION_MAJOR) "." ETL_STRINGIFY(ETL_VERSION_MINOR) "." ETL_STRINGIFY(ETL_VERSION_PATCH)
 #define ETL_VERSION_W     ETL_STRINGIFY(ETL_VERSION_MAJOR) L"." ETL_STRINGIFY(ETL_VERSION_MINOR) L"." ETL_STRINGIFY(ETL_VERSION_PATCH)
 #define ETL_VERSION_U16   ETL_STRINGIFY(ETL_VERSION_MAJOR) u"." ETL_STRINGIFY(ETL_VERSION_MINOR) u"." ETL_STRINGIFY(ETL_VERSION_PATCH)
diff --git a/library.json b/library.json
index 524a76a9..f1494e89 100644
--- a/library.json
+++ b/library.json
@@ -1,6 +1,6 @@
 {
   "name": "Embedded Template Library",
-  "version": "18.4.0",
+  "version": "18.5.0",
   "authors": {
     "name": "John Wellbelove",
     "email": "john.wellbelove@etlcpp.com"
diff --git a/library.properties b/library.properties
index a3580b7c..1522a6f5 100644
--- a/library.properties
+++ b/library.properties
@@ -1,5 +1,5 @@
 name=Embedded Template Library
-version=18.4.0
+version=18.5.0
 author= John Wellbelove <john.wellbelove@etlcpp.com>
 maintainer=John Wellbelove <john.wellbelove@etlcpp.com>
 license=MIT
diff --git a/support/Release notes.txt b/support/Release notes.txt
index 7e7c253e..9ba7af3b 100644
--- a/support/Release notes.txt	
+++ b/support/Release notes.txt	
@@ -1,3 +1,17 @@
+===============================================================================
+18.5.0
+Added string streams
+etl::string_stream
+etl::wstring_stream
+etl::u16string_stream
+etl::u32string_stream
+
+Added string formatting to etl::to_string from
+etl::string etl::string_view
+etl::wstring etl::wstring_view
+etl::u16string etl::u16string_view
+etl::u32string etl::u32string_view
+
 ===============================================================================
 18.4.0
 Refactored etl::error_handler to use etl::delegate style implementation.