[Sunrisepeak]

The C standard library as C++23 modules: mcpplibs.mwrap.libc 17.0.0 maps the object-like macros of ISO C17 that std.compat cannot export (a named module exports no macro). mcpp 2026.11.7.1, mcpp-plugins and the language server read stdout, stderr, EOF, BUFSIZ and errno from it instead of including C headers for their macros (mcpp design record 2026-11-07, D10, §4.4.1).

Contents

• mcpplibs.mwrap.libc: export import std.compat; and the macros module.
• mcpplibs.mwrap.libc.macros: every object-like macro of ISO C17 Annex B that the target defines (tools/iso_c.toml, 334 names; 331 on glibc): 315 constant expressions as inline constexpr; the rest as constexpr functions returning the macro's expression (errno() is int&, stdout() the stream, MB_CUR_MAX()); eight that are constants only with some C libraries take the function form everywhere (tools/surface.toml). Each mapping exists where the target defines the macro (#ifdef).
• <mwrap/libc/macros.hpp>: includes <assert.h>, <setjmp.h>, <stdarg.h>, <stddef.h>, <stdint.h> for assert, setjmp, va_*, offsetof, INTn_C.
• Not mapped, with reasons (docs/usage.md): POSIX error numbers (std::errc), NULL, C-only headers, keyword macros, classification macros, __STDC_*, Annex K.
• Version 17.0.0 names ISO/IEC 9899:2018, which C++23 references; [package.metadata.mwrap] records the standard and that the implementation is the target's C library. The release check accepts a standard as upstream without retained documents.
• CI: glibc with libstdc++ and libc++, musl, openkal-musl under okrun, macOS libSystem, the Windows CRT with libc++ and the MSVC STL, mingw-w64. Tests write through stdout()/stderr(), read errno() as set by strtol, use the stdio constants, call the function-like macros, compare every mapping with its macro, and mix the header with the module. Default template stdio.

Local results (Linux x86_64)

Check	Result
mcpp test, GCC 16.1.0 / LLVM 23.1.3 / --target x86_64-linux-musl / --target x86_64-openkal --platform openkal-platform@0.24.0	3/3 passed each; 331 macros mapped, 0 differ
tools/generate.py --check	0 problems
tools/test_template.py	template built and ran
tools/check_mwrap_release.py	mcpplibs.mwrap.libc@17.0.0

After merge: tag mwrap-17.0.0, GitCode mirror, mcpp-index pkgs/mwrap/libc.lua, tests/mwrap/libc, and the sentence in docs/mwrap.md that the C standard library's implementation is the target's C library.