codecvt_utf8_utf16/std::wstring_convert is deprecated

src/libipc/platform/to_tchar.h

@@ -1,12 +1,14 @@
 #pragma once
 
-#include <tchar.h>
+#include <Windows.h>
 
 #include <type_traits>
 #include <string>
 #include <locale>
 #include <codecvt>
 #include <cstring>
+#include <stdexcept>
+#include <cstddef>
 
 #include "libipc/utility/concept.h"
 #include "libipc/platform/detail.h"
@@ -35,33 +37,67 @@ using IsSameChar = ipc::require<is_same_char<T, S>::value, R>;
 
 template <typename T = TCHAR>
 constexpr auto to_tchar(ipc::string &&str) -> IsSameChar<T, ipc::string, ipc::string &&> {
-    return std::move(str);
+    return std::move(str); // noconv
 }
 
+/**
+ * codecvt_utf8_utf16/std::wstring_convert is deprecated
+ * @see https://codingtidbit.com/2020/02/09/c17-codecvt_utf8-is-deprecated/
+ *      https://stackoverflow.com/questions/42946335/deprecated-header-codecvt-replacement
+ *      https://en.cppreference.com/w/cpp/locale/codecvt/in
+ *      https://docs.microsoft.com/en-us/windows/win32/api/stringapiset/nf-stringapiset-multibytetowidechar
+*/
 template <typename T = TCHAR>
-constexpr auto to_tchar(ipc::string && str) -> IsSameChar<T, ipc::wstring> {
-    return std::wstring_convert<
-        std::codecvt_utf8_utf16<wchar_t>,
-        wchar_t,
-        ipc::mem::allocator<wchar_t>,
-        ipc::mem::allocator<char>
-    >{}.from_bytes(std::move(str));
+auto to_tchar(ipc::string &&external) -> IsSameChar<T, ipc::wstring> {
+    if (external.empty()) {
+        return {}; // noconv
     }
-
-template <typename T>
-inline auto to_tchar(T* dst, char const * src, std::size_t size) -> IsSameChar<T, char, void> {
-    std::memcpy(dst, src, size);
+#if 0 // backup
+    auto &fcodecvt = std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(std::locale());
+    std::mbstate_t mb {};
+    ipc::wstring internal(external.size(), '\0');
+    char const *first = &external[0], *last = &external[external.size()];
+    std::size_t len   = 0;
+    while (first != last) {
+        wchar_t *start = &internal[len], *end = &internal[internal.size()], *to_next;
+        auto ret = fcodecvt.in(mb, first, last, first,
+                                   start, end , to_next);
+        switch (ret) {
+        // no conversion, just copy code values
+        case std::codecvt_base::noconv:
+            internal.resize(len);
+            for (; first != last; ++first) {
+                internal.push_back((wchar_t)(unsigned char)*first);
             }
-
-template <typename T>
-inline auto to_tchar(T* dst, char const * src, std::size_t size) -> IsSameChar<T, wchar_t, void> {
-    auto wstr = std::wstring_convert<
-        std::codecvt_utf8_utf16<wchar_t>,
-        wchar_t,
-        ipc::mem::allocator<wchar_t>,
-        ipc::mem::allocator<char>
-    >{}.from_bytes(src, src + size);
-    std::memcpy(dst, wstr.data(), (ipc::detail::min)(wstr.size(), size));
+            break;
+        // conversion completed
+        case std::codecvt_base::ok:
+            len += static_cast<size_t>(to_next - start);
+            internal.resize(len);
+            break;
+        // not enough space in the output buffer or unexpected end of source buffer
+        case std::codecvt_base::partial:
+            if (to_next <= start) {
+                throw std::range_error{"[to_tchar] bad conversion"};
+            }
+            len += static_cast<size_t>(to_next - start);
+            internal.resize(internal.size() + external.size());
+            break;
+        // encountered a character that could not be converted
+        default: // error
+            throw std::range_error{"[to_tchar] bad conversion"};
+        }
+    }
+#else
+    // CP_ACP: The system default Windows ANSI code page.
+    int size_needed = ::MultiByteToWideChar(CP_ACP, 0, &external[0], (int)external.size(), NULL, 0);
+    if (size_needed <= 0) {
+        return {};
+    }
+    ipc::wstring internal(size_needed, L'\0');
+    ::MultiByteToWideChar(CP_ACP, 0, &external[0], (int)external.size(), &internal[0], size_needed);
+#endif
+    return internal;
 }
 
 } // namespace detail

test/test_platform.cpp

@@ -0,0 +1,28 @@
+
+#if defined(WIN64) || defined(_WIN64) || defined(__WIN64__) || \
+    defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(__NT__) || \
+    defined(WINCE) || defined(_WIN32_WCE)
+
+#include <locale>
+#include <iostream>
+
+#include "test.h"
+
+#include "libipc/platform/to_tchar.h"
+
+TEST(Platform, to_tchar) {
+    char    const *utf8 =  "hello world, 低挫<E4BD8E>こんにちは";
+    wchar_t const *wstr = L"hello world, 低挫<E4BD8E>こんにちは";
+    {
+        ipc::string str = ipc::detail::to_tchar<char>(utf8);
+        EXPECT_STREQ(str.c_str(), utf8);
+    }
+    {
+        ipc::wstring wtr = ipc::detail::to_tchar<wchar_t>(utf8);
+        //std::wcout.imbue(std::locale());
+        //std::wcout << wtr << "\n";
+        EXPECT_STREQ(wtr.c_str(), wstr);
+    }
+}
+
+#endif/*WIN*/