etl/docs/strings/string_stream.md
John Wellbelove 4a88884b39
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---------

Co-authored-by: Roland Reichwein <Roland.Reichwein@bmw.de>
Co-authored-by: John Wellbelove <john.wellbelove@etlcpp.com>
Co-authored-by: John Wellbelove <john.wellbelove@etlcpp.co.uk>
2026-06-06 13:12:44 +01:00

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Markdown

---
title: "string_stream"
---
{{< callout type="info">}}
Header: `string_stream.h`
{{< /callout >}}
## Streaming types
`string_stream`
`wstring_stream`
`u16string_stream`
`u32string_stream`
Classes to build strings using a streaming API.
Uses `etl::basic_format_spec` to define the required formatting.
The documentation below is for `etl::string_stream`.
The other streams have a similar API, though using `w`, `u8`, `u16` or `u32` types.
## Member functions
```cpp
explicit string_stream(etl::istring& str)
```
**Description**
Construct, using the supplied string as a buffer.
Uses the default `format_spec`.
---
```cpp
string_stream(etl::istring& str, const etl::format_spec& spec)
```
**Description**
Construct, using the supplied string as a buffer.
Initialised with the supplied `format_spec`.
---
```cpp
void set_format(const etl::format_spec& spec_)
```
**Description**
Sets a new `format_spec` to use.
---
```cpp
const etl::format_spec& get_format() const
```
**Description**
Gets the current `format_spec`.
---
```cpp
etl::istring& str()
```
**Description**
Gets a reference to the internal string.
```cpp
const etl::istring& str() const
```
**Description**
Gets a const reference to the internal string.
---
```cpp
void str(const etl::istring::const_pointer p)
```
**Description**
Resets the internal string to the text pointed to by `p`.
---
```cpp
void str(const etl::istring& text)
```
**Description**
Resets the internal string to `text`.
## Streaming operators
```cpp
string_stream& operator <<(string_stream& ss, T value)
```
**Description**
Where `T` may be one of the following:-
Any fundamental type.
`etl::format_spec`
`etl::setb0ase(n)`
`etl::bin`
`etl::oct`
`etl::dec`
`etl::hex`
`etl::setfill(c)`
`etl::setw(n)`
`etl::setprecision(n)`
`etl::left`
`etl::right`
`etl::boolalpha`
`etl::noboolalpha`
`etl::uppercase`
`etl::nouppercase`
`etl::showbase`
`etl::noshowbase`
`etl::string`
`etl::istring`
`etl::string_view`
`const char*`
See `etl::format_spec`
Custom user types may be streamed by overloading the streaming operator.
## Examples
### Using format_spec
```cpp
etl::format_spec format1 = etl::format_spec().hex().width(8).fill('0');
etl::format_spec format2;
etl::format_spec format3 = etl::format_spec().width(6).fill('#').precision(3);
etl::string<50> text;
etl::string_stream stream(text);
stream << format1 << 1193046 << format2 << " " << format3 << 3.1415;
const etl::istring& result = stream.str();
```
`text` is set to `"00123456 #3.142"`.
### Using stream manipulators
```cpp
etl::string<50> text;
etl::string_stream stream(text);
stream << etl::hex << etl::setw(8) << etl::setfill('0') << 1193046
<< etl::setw(0) << " "
<< etl::setw(6) << etl::setfill('#') << etl::setprecision(3) << 3.1415;
const etl::istring& result = stream.str();
```
`text` is set to `"00123456 #3.142"`.