Trying std::format

December 7, 2022

I am trying to test std::format, but, unfortunately, it is not fully available in gcc nor clang. I know, I know, I could use fmt instead, but I need std::format because they are not identical.

For the record, what I have done is:

Get the latest llvm sources
Build libc++, and company, enabling the experimental features ¹
Install it under /opt/clang/16/

git clone https://github.com/llvm/llvm-project.git --depth 1
cd llvm-project
cmake -G Ninja -S llvm -B build \
    -DLLVM_ENABLE_PROJECTS="clang" \
    -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
    -DLIBCXX_ENABLE_INCOMPLETE_FEATURES=ON \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=/opt/clang/16/
ninja -C build runtimes
ninja -C build install-cxx install-cxxabi install-unwind

Once that is done, I configure the test project with the following flags:

cmake \
    -DCMAKE_CXX_FLAGS="-nostdinc++ -nostdlib++ -fexperimental-library \
        -isystem /opt/clang/16/include/c++/v1 \
        -isystem /opt/clang/16/include/x86_64-unknown-linux-gnu/c++/v1" \
    -DCMAKE_EXE_LINKER_FLAGS="-L /opt/clang/16/lib/x86_64-unknown-linux-gnu\
        -Wl,-rpath,/opt/clang/16/lib/x86_64-unknown-linux-gnu\
        -lc++ -fuse-ld=lld -lc++experimental"

Note that the system default linker (bfd) didn’t work, so I had to use lld instead. I am (still) running an Ubuntu 20.04 at work.

With that, #include <format> works 😄

Building libc++ ↩︎