Implementation of P2146 - Modern std::byte stream IO for C++

Reference implementation of P2146 - Modern std::byte stream IO for C++.

None of the major compilers support all of the C++20 features required to implement this proposal. The missing features are:

• GCC: std::bit_cast.
• Clang: concepts library, ranges, std::bit_cast.
• MSVC: ranges.

Component	Implementation status
std::io::make_error_code	✅
std::io::make_error_condition	✅
std::io::category	Partial
std::io::io_error	Partial
std::io::offset	✅
std::io::position	✅
std::io::input_stream	✅
std::io::output_stream	✅
std::io::stream	✅
std::io::input_output_stream	✅
std::io::seekable_stream	✅
std::io::buffered_stream	✅
std::io::read_raw	✅
std::io::write_raw	✅
std::io::format	✅
std::io::context	✅
std::io::input_context	✅
std::io::output_context	✅
std::io::default_context	✅
std::io::read	Partial
std::io::write	Partial
std::io::readable_from	✅
std::io::writable_to	✅
std::io::any_input_stream	✅
std::io::any_output_stream	✅
std::io::any_input_output_stream	✅
std::io::in	Partial
std::io::out	Partial
std::io::err	Partial
std::io::input_span_stream	✅
std::io::output_span_stream	✅
std::io::input_output_span_stream	✅
std::io::basic_input_memory_stream	✅
std::io::basic_output_memory_stream	✅
std::io::basic_input_output_memory_stream	✅
std::io::input_file_stream	Partial
std::io::output_file_stream	Partial
std::io::input_output_file_stream	Partial

Notes on floating point support

std::io::floating_point_format::native is supported everywhere.

Full std::io::floating_point_format::iec559 functionality requires mainstream endianness, native ISO 60559 types and lack of padding bits.

• Only binary32 and binary64 formats without padding bits are supported right now.
• Assuming the previous point, std::endian::native is supported regardless of its value.
• Otherwise, only byte swaps are supported (little to big, big to little). This requires std::endian::native to be either std::endian::little or std::endian::big.

Notes on file IO and standard stream objects

• Only POSIX and Windows are supported right now.
• If a POSIX or Windows call produces the error that is not in the proposal, std::system_error is thrown.

POSIX specific notes

• std::io::creation::always_new does not have direct equivalent in POSIX and is implemented using std::filesystem which suffers from TOCTOU.

Windows specific notes

• File buffer size is hardcoded to 4096.
• Standard stream objects are not thread-safe yet.

How to build

General build dependencies:

• Git
• CMake 3.12 or newer

Linux

Step 1: Create build directory and change into it

mkdir Build
cd Build

Step 2: Configure CMake with your choice of compiler and standard library

GCC and libstdc++

Requires at least GCC 10.2.

Assuming g++-trunk is not default compiler but it is the latest version you want:

cmake -D CMAKE_CXX_COMPILER=g++-trunk ..

Clang and libstdc++

Requires at least Clang 10 and libstdc++ shipped with GCC 10.2.

Assuming clang++ is not default compiler but it is the latest version you want:

cmake -D CMAKE_CXX_COMPILER=clang++ ..

Clang and libc++

Not usable right now because of lack of concepts library.

Assuming clang++ is not default compiler but it is the latest version you want:

cmake -D CMAKE_CXX_COMPILER=clang++ -D CMAKE_CXX_FLAGS=-stdlib=libc++ ..

Step 3: Build the library

cmake --build .

Windows

Mingw-w64 on Linux (cross-compiling)

Requires at least GCC 10.2.

Assuming x86_64-w64-mingw32-g++ is the compiler you want:

mkdir Build
cd Build
cmake -D CMAKE_SYSTEM_NAME=Windows -D CMAKE_CXX_COMPILER=x86_64-w64-mingw32-g++ ..
cmake --build .

MSVC

Not supported yet.