pw_minimal_cpp_stdlib#

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Do not use this module unless you have consulted with the Pigweed team.

Maintenance#

If you discovered this module because of a build failure in a pw_strict_host_clang_size_optimized_minimal_cpp_stdlib or similar target, the important thing to know is that a small set of Pigweed targets are expected to compile using a limited set of C++ Standard Library features and headers that have been polyfilled by this module in order to support environments without a C++ stdlib.

Failed #include lines should be solved by either eliminating the dependency from the target (strongly preferred) or by adding a (minimal) polyfill of the relevant C++ header to this module.

Polyfills may assume a C++17 (or greater) compiler but with only a C (not C++) stdlib. As this target does not support tests, polyfills can only be checked for compilation; this can be done by building the root build_with_pw_minimal_cpp_stdlib group (e.g. ninja -C out build_with_pw_minimal_cpp_stdlib).

Purpose#

The pw_minimal_cpp_stdlib module provides an extremely limited, incomplete implementation of the C++ Standard Library. This module is only intended for testing and development when compiling with C++17 or newer, but without access to the C++ Standard Library (-nostdinc++).

Production code should use a real C++ Standard Library implementation, such as libc++ or libstdc++.

Warning

pw_minimal_cpp_stdlib was created for a very specific purpose. It is NOT a general purpose C++ Standard Library implementation and should not be used as one.

  • Many library features are missing.

  • Many features are non-functioning stubs.

  • Some features do not match the C++ standard.

  • Test coverage is extremely limited.

Build integration#

The top-level build_with_minimal_cpp_stdlib GN group builds a few supported modules with pw_minimal_cpp_stdlib swapped in for the C++ library at the toolchain level. Notably, pw_minimal_cpp_stdlib does not support pw_unit_test, so this group does NOT run any tests.

Code layout#

The C++ Standard Library headers (e.g. <cstdint> and <type_traits>) are defined in public/. These files are symlinks to their implementations in public/internal/.

Tip

You can automatically recreate the symlinks in public/ by executing the following Bash code from pw_minimal_cpp_stdlib/public/.

for f in $(ls pw_minimal_cpp_stdlib/internal/); do ln -s pw_minimal_cpp_stdlib/internal/$f ${f%.h}; done

Requirements#

  • C++17

  • gcc or clang

  • The C Standard Library

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