如何使用cmake确保C ++ 14编译器与实验性文件系统TS库链接？

Question

I'm (switching to) using <std::experimental::filesystem> in my C++14 code, and I need to be able to build it using GCC 5.x on Linux (and any C++14-enabled compiler really, or at least - relevant versions of clang, msvc and perhaps icc) .

Now, when I link, I'm getting errors about missing all of the filesystem-related symbols, eg:

foo.cpp:(.text+0x9cd): undefined reference to `std::experimental::filesystem::v1::__cxx11::path::_M_split_cmpts()'

Now, if I "manually" add a dependency on libstdc++fs :

target_link_libraries(foo other_lib stdc++fs)

then everything links fine - but how do I generalize this to any C++14-capable compiler?

Note: The relevant parts of my CMakeLists.txt look something like this:

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall" )
set(CMAKE_CXX_STANDARD 14)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

add_library(bar src/bar.cpp)
add_executable(foo src/foo.cpp)
target_link_libraries(foo bar other_lib)

---

_{* (When I was using boost::filesystem it was paradoxically easier - I just need to use whatever FindBoost.cmake produced.)
** Using -Wall is a problem for other compilers as well, I guess.}

Answer 1

Unfortunately, this is exactly how it is intended to be used. See the relevant part of libstdc++ documentation :

GCC 5.3 includes an implementation of the Filesystem library defined by the technical specification ISO/IEC TS 18822:2015. Because this is an experimental library extension, not part of the C++ standard, it is implemented in a separate library, libstdc++fs.a, and there is no shared library for it. To use the library you should include and link with -lstdc++fs . The library implementation is incomplete on non-POSIX platforms, specifically Windows support is rudimentary.

Due to the experimental nature of the Filesystem library the usual guarantees about ABI stability and backwards compatibility do not apply to it. There is no guarantee that the components in any header will remain compatible between different GCC releases.

(emphasis mine)

To link libstdc++fs explicitly only under GCC, you can use the relevant CMake variable :

target_link_libraries(foo other_lib)
if (CMAKE_CXX_COMPILER_ID STREQUAL GNU)
    target_link_libraries(foo stdc++fs)
endif()

Or, in a bit fancier manner,

if (CMAKE_CXX_COMPILER_ID STREQUAL GNU)
    set(CXX_FILESYSTEM_LIBRARIES stdc++fs)
else()
    set(CXX_FILESYSTEM_LIBRARIES)
endif()
target_link_libraries(foo other_lib ${CXX_FILESYSTEM_LIBRARIES})