C++ Format v5.0.0 release notes (2018-05-21)

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C++ Format v5.0.0 Release Notes

Release Date: 2018-05-21 // almost 6 years ago

- ➕ Added a requirement for partial C++11 support, most importantly variadic templates and type traits, and dropped FMT_VARIADIC_* emulation macros. Variadic templates are available since GCC 4.4, Clang 2.9 and MSVC 18.0 (2013). For older compilers use {fmt} version 4.x <https://github.com/fmtlib/fmt/releases/tag/4.1.0>_ which continues to be maintained and works with C++98 compilers.
- 📇 Renamed symbols to follow standard C++ naming conventions and proposed a subset of the library for standardization in P0645R2 Text Formatting <https://wg21.link/P0645>_.
- 📜 Implemented constexpr parsing of format strings and compile-time format string checks <https://fmt.dev/latest/api.html#compile-time-format-string-checks>_. For example
.. code:: c++
```
 #include <fmt/format.h>

 std::string s = format(fmt("{:d}"), "foo");
```
gives a compile-time error because d is an invalid specifier for strings (godbolt <https://godbolt.org/g/rnCy9Q>__)::
```
 ...
 <source>:4:19: note: in instantiation of function template specialization 'fmt::v5::format<S, char [4]>' requested here
   std::string s = format(fmt("{:d}"), "foo");
                   ^
 format.h:1337:13: note: non-constexpr function 'on_error' cannot be used in a constant expression
     handler.on_error("invalid type specifier");
```
Compile-time checks require relaxed constexpr (C++14 feature) support. If the latter is not available, checks will be performed at runtime.
- 📜 Separated format string parsing and formatting in the extension API to enable compile-time format string processing. For example
.. code:: c++
```
 struct Answer {};

 namespace fmt {
 template <>
 struct formatter<Answer> {
   constexpr auto parse(parse_context& ctx) {
     auto it = ctx.begin();
     spec = *it;
     if (spec != 'd' && spec != 's')
       throw format_error("invalid specifier");
     return ++it;
   }

   template <typename FormatContext>
   auto format(Answer, FormatContext& ctx) {
     return spec == 's' ?
       format_to(ctx.begin(), "{}", "fourty-two") :
       format_to(ctx.begin(), "{}", 42);
   }

   char spec = 0;
 };
 }

 std::string s = format(fmt("{:x}"), Answer());
```
gives a compile-time error due to invalid format specifier (godbolt <https://godbolt.org/g/2jQ1Dv>__)::
```
 ...
 <source>:12:45: error: expression '<throw-expression>' is not a constant expression
        throw format_error("invalid specifier");
```
- ➕ Added iterator support <https://fmt.dev/latest/api.html#output-iterator-support>_:
.. code:: c++
```
 #include <vector>
 #include <fmt/format.h>

 std::vector<char> out;
 fmt::format_to(std::back_inserter(out), "{}", 42);
```
- Added the format_to_n <https://fmt.dev/latest/api.html#_CPPv2N3fmt11format_to_nE8OutputItNSt6size_tE11string_viewDpRK4Args>_ function that restricts the output to the specified number of characters (#298 <https://github.com/fmtlib/fmt/issues/298>_):
.. code:: c++
```
 char out[4];
 fmt::format_to_n(out, sizeof(out), "{}", 12345);
 // out == "1234" (without terminating '\0')
```
- ➕ Added the formatted_size <https://fmt.dev/latest/api.html#_CPPv2N3fmt14formatted_sizeE11string_viewDpRK4Args>_ function for computing the output size:
.. code:: c++
```
 #include <fmt/format.h>

 auto size = fmt::formatted_size("{}", 12345); // size == 5
```
- 👌 Improved compile times by reducing dependencies on standard headers and providing a lightweight core API <https://fmt.dev/latest/api.html#core-api>_:
.. code:: c++
```
 #include <fmt/core.h>

 fmt::print("The answer is {}.", 42);
```
See Compile time and code bloat <https://github.com/fmtlib/fmt#compile-time-and-code-bloat>_.
- Added the make_format_args <https://fmt.dev/latest/api.html#_CPPv2N3fmt16make_format_argsEDpRK4Args>_ function for capturing formatting arguments:
.. code:: c++
```
 // Prints formatted error message.
 void vreport_error(const char *format, fmt::format_args args) {
   fmt::print("Error: ");
   fmt::vprint(format, args);
 }
 template <typename... Args>
 void report_error(const char *format, const Args & ... args) {
   vreport_error(format, fmt::make_format_args(args...));
 }
```
- 🖨 Added the make_printf_args function for capturing printf arguments (#687 <https://github.com/fmtlib/fmt/issues/687>, #694 <https://github.com/fmtlib/fmt/pull/694>). Thanks @Kronuz (Germán Méndez Bravo) <https://github.com/Kronuz>_.
- ➕ Added prefix v to non-variadic functions taking format_args to distinguish them from variadic ones:
.. code:: c++
```
 std::string vformat(string_view format_str, format_args args);

 template <typename... Args>
 std::string format(string_view format_str, const Args & ... args);
```
- ➕ Added experimental support for formatting ranges, containers and tuple-like types in fmt/ranges.h (#735 <https://github.com/fmtlib/fmt/pull/735>_):
.. code:: c++
```
 #include <fmt/ranges.h>

 std::vector<int> v = {1, 2, 3};
 fmt::print("{}", v); // prints {1, 2, 3}
```
Thanks @Remotion (Remo) <https://github.com/Remotion>_.
- Implemented wchar_t date and time formatting (#712 <https://github.com/fmtlib/fmt/pull/712>_):
.. code:: c++
```
 #include <fmt/time.h>

 std::time_t t = std::time(nullptr);
 auto s = fmt::format(L"The date is {:%Y-%m-%d}.", *std::localtime(&t));
```
Thanks @DanielaE (Daniela Engert) <https://github.com/DanielaE>_.
- Provided more wide string overloads (#724 <https://github.com/fmtlib/fmt/pull/724>). Thanks @DanielaE (Daniela Engert) <https://github.com/DanielaE>.
- Switched from a custom null-terminated string view class to string_view in the format API and provided fmt::string_view which implements a subset of std::string_view API for pre-C++17 systems.
- ➕ Added support for std::experimental::string_view (#607 <https://github.com/fmtlib/fmt/pull/607>_):
.. code:: c++
```
 #include <fmt/core.h>
 #include <experimental/string_view>

 fmt::print("{}", std::experimental::string_view("foo"));
```
Thanks @virgiliofornazin (Virgilio Alexandre Fornazin) <https://github.com/virgiliofornazin>__.
- 👍 Allowed mixing named and automatic arguments:
.. code:: c++
```
 fmt::format("{} {two}", 1, fmt::arg("two", 2));
```
- ✂ Removed the write API in favor of the format API <https://fmt.dev/latest/api.html#format-api>_ with compile-time handling of format strings.
- Disallowed formatting of multibyte strings into a wide character target (#606 <https://github.com/fmtlib/fmt/pull/606>_).
- 👌 Improved documentation (#515 <https://github.com/fmtlib/fmt/pull/515>, #614 <https://github.com/fmtlib/fmt/issues/614>, #617 <https://github.com/fmtlib/fmt/pull/617>, #661 <https://github.com/fmtlib/fmt/pull/661>, #680 <https://github.com/fmtlib/fmt/pull/680>). Thanks @ibell (Ian Bell) <https://github.com/ibell>, @mihaitodor (Mihai Todor) <https://github.com/mihaitodor>, and @johnthagen <https://github.com/johnthagen>.
- Implemented more efficient handling of large number of format arguments.
- Introduced an inline namespace for symbol versioning.
- ➕ Added debug postfix d to the fmt library name (#636 <https://github.com/fmtlib/fmt/issues/636>_).
- ✂ Removed unnecessary fmt/ prefix in includes (#397 <https://github.com/fmtlib/fmt/pull/397>). Thanks @chronoxor (Ivan Shynkarenka) <https://github.com/chronoxor>.
- Moved fmt/*.h to include/fmt/*.h to prevent irrelevant files and directories appearing on the include search paths when fmt is used as a subproject and moved source files to the src directory.
- ➕ Added qmake project file support/fmt.pro (#641 <https://github.com/fmtlib/fmt/pull/641>). Thanks @cowo78 (Giuseppe Corbelli) <https://github.com/cowo78>.
- ➕ Added Gradle build file support/build.gradle (#649 <https://github.com/fmtlib/fmt/pull/649>). Thanks @luncliff (Park DongHa) <https://github.com/luncliff>.
- ✂ Removed FMT_CPPFORMAT CMake option.
- 🛠 Fixed a name conflict with the macro CHAR_WIDTH in glibc (#616 <https://github.com/fmtlib/fmt/pull/616>). Thanks @aroig (Abdó Roig-Maranges) <https://github.com/aroig>.
- 🛠 Fixed handling of nested braces in fmt::join (#638 <https://github.com/fmtlib/fmt/issues/638>_).
- ➕ Added SOURCELINK_SUFFIX for compatibility with Sphinx 1.5 (#497 <https://github.com/fmtlib/fmt/pull/497>). Thanks @ginggs (Graham Inggs) <https://github.com/ginggs>.
- ➕ Added a missing inline in the header-only mode (#626 <https://github.com/fmtlib/fmt/pull/626>). Thanks @aroig (Abdó Roig-Maranges) <https://github.com/aroig>.
- 🛠 Fixed various compiler warnings (#640 <https://github.com/fmtlib/fmt/pull/640>, #656 <https://github.com/fmtlib/fmt/pull/656>, #679 <https://github.com/fmtlib/fmt/pull/679>, #681 <https://github.com/fmtlib/fmt/pull/681>, #705 <https://github.com/fmtlib/fmt/pull/705>_, #715 <https://github.com/fmtlib/fmt/issues/715>, #717 <https://github.com/fmtlib/fmt/pull/717>, #720 <https://github.com/fmtlib/fmt/pull/720>, #723 <https://github.com/fmtlib/fmt/pull/723>, #726 <https://github.com/fmtlib/fmt/pull/726>, #730 <https://github.com/fmtlib/fmt/pull/730>, #739 <https://github.com/fmtlib/fmt/pull/739>). Thanks @peterbell10 <https://github.com/peterbell10>, @LarsGullik <https://github.com/LarsGullik>, @foonathan (Jonathan Müller) <https://github.com/foonathan>, @eliaskosunen (Elias Kosunen) <https://github.com/eliaskosunen>, @christianparpart (Christian Parpart) <https://github.com/christianparpart>, @DanielaE (Daniela Engert) <https://github.com/DanielaE>, and @mwinterb <https://github.com/mwinterb>_.
- ⚠ Worked around an MSVC bug and fixed several warnings (#653 <https://github.com/fmtlib/fmt/pull/653>). Thanks @alabuzhev (Alex Alabuzhev) <https://github.com/alabuzhev>.
- Worked around GCC bug 67371 (#682 <https://github.com/fmtlib/fmt/issues/682>_).
- 🛠 Fixed compilation with -fno-exceptions (#655 <https://github.com/fmtlib/fmt/pull/655>). Thanks @chenxiaolong (Andrew Gunnerson) <https://github.com/chenxiaolong>.
- 🚚 Made constexpr remove_prefix gcc version check tighter (#648 <https://github.com/fmtlib/fmt/issues/648>_).
- 📇 Renamed internal type enum constants to prevent collision with poorly written C libraries (#644 <https://github.com/fmtlib/fmt/issues/644>_).
- ➕ Added detection of wostream operator<< (#650 <https://github.com/fmtlib/fmt/issues/650>_).
- 🛠 Fixed compilation on OpenBSD (#660 <https://github.com/fmtlib/fmt/pull/660>). Thanks @hubslave <https://github.com/hubslave>.
- 🛠 Fixed compilation on FreeBSD 12 (#732 <https://github.com/fmtlib/fmt/pull/732>). Thanks @dankm <https://github.com/dankm>.
- 🛠 Fixed compilation when there is a mismatch between -std options between the library and user code (#664 <https://github.com/fmtlib/fmt/issues/664>_).
- 🛠 Fixed compilation with GCC 7 and -std=c++11 (#734 <https://github.com/fmtlib/fmt/issues/734>_).
- 👌 Improved generated binary code on GCC 7 and older (#668 <https://github.com/fmtlib/fmt/issues/668>_).
- 🛠 Fixed handling of numeric alignment with no width (#675 <https://github.com/fmtlib/fmt/issues/675>_).
- 🛠 Fixed handling of empty strings in UTF8/16 converters (#676 <https://github.com/fmtlib/fmt/pull/676>). Thanks @vgalka-sl (Vasili Galka) <https://github.com/vgalka-sl>.
- 🛠 Fixed formatting of an empty string_view (#689 <https://github.com/fmtlib/fmt/issues/689>_).
- 🛠 Fixed detection of string_view on libc++ (#686 <https://github.com/fmtlib/fmt/issues/686>_).
- 🛠 Fixed DLL issues (#696 <https://github.com/fmtlib/fmt/pull/696>). Thanks @sebkoenig <https://github.com/sebkoenig>.
- 🛠 Fixed compile checks for mixing narrow and wide strings (#690 <https://github.com/fmtlib/fmt/issues/690>_).
- Disabled unsafe implicit conversion to std::string (#729 <https://github.com/fmtlib/fmt/issues/729>_).
- 🛠 Fixed handling of reused format specs (as in fmt::join) for pointers (#725 <https://github.com/fmtlib/fmt/pull/725>). Thanks @mwinterb <https://github.com/mwinterb>.
- 🛠 Fixed installation of fmt/ranges.h (#738 <https://github.com/fmtlib/fmt/pull/738>). Thanks @sv1990 <https://github.com/sv1990>.

C++ Format v5.0.0

Version Release Notes from May 21, 2018 (almost 6 years ago)

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C++ Format v5.0.0 Release Notes