Issue
I'm playing around with developing a cross-platform C++ project. Things build fine on Linux, but on Windows (10) + MSys2 I've run into a strange issue. Compile works fine (picks up my include dirs, etc.), but linking fails with all sorts of undefined reference errors to a static imported library I have, and even the C++ runtime.
I've tried setting CMAKE_C[XX]_COMPILER, CMAKE_MAKE_PROGRAM, but the output from the configuration step is always the same:
$ cmake ..
-- The C compiler identification is GNU 10.2.0
-- The CXX compiler identification is GNU 10.2.0
System is unknown to cmake, create:
Platform/MINGW64_NT-10.0-19041 to use this system, please post your config file on discourse.cmake.org so it can be added to cmake
-- Detecting C compiler ABI info
System is unknown to cmake, create:
Platform/MINGW64_NT-10.0-19041 to use this system, please post your config file on discourse.cmake.org so it can be added to cmake
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /mingw64/bin/cc.exe - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
System is unknown to cmake, create:
Platform/MINGW64_NT-10.0-19041 to use this system, please post your config file on discourse.cmake.org so it can be added to cmake
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /mingw64/bin/CC.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: <....>
As mentioned earlier the compile works, but linking the executable fails spectacularly. Here is my minimal working example:
$ cat ../CMakeLists.txt
project(example)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED True)
add_executable(example
main.cpp
)
Here is an sample of the output (the rest is omitted for brevity):
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.cpp.obj:main.cpp:(.text+0x51): undefined reference to `std::ios_base::Init::~Init()'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.cpp.obj:main.cpp:(.text+0x81): undefined reference to `std::ios_base::Init::Init()'
Adding -v to cmake produces the following commands.
Compile:
/mingw64/bin/CC.exe -std=gnu++17 -o CMakeFiles/example.dir/main.cpp.obj -c /home/.../Development/minex/main.cpp
Link:
/mingw64/bin/CC.exe CMakeFiles/example.dir/main.cpp.obj -o example
CC.exe seems off... and it's used if I set the CXX compiler flag or not...
I also tried generating "MSYS2 Makefiles" but that also fails (doesn't know the generator).
I can reproduce the output by running
$ CC main.cpp -o example
while
$ g++ main.cpp -o example
works fine.
CMake version is 3.18.4.
Edit: This is the entire output of running make VERBOSE=1 (using mingw64-cmake seems to produce the same output, except the 'entering directory' and 'leaving directory' paths are absolute windows paths):
$ cat log
/usr/bin/cmake.exe -S/home/<...>/Development/minex -B/home/<...>/Development/minex/build --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake.exe -E cmake_progress_start /home/<...>/Development/minex/build/CMakeFiles /home/<...>/Development/minex/build//CMakeFiles/progress.marks
make -f CMakeFiles/Makefile2 all
make[1]: Entering directory '/home/<...>/Development/minex/build'
make -f CMakeFiles/example.dir/build.make CMakeFiles/example.dir/depend
make[2]: Entering directory '/home/<...>/Development/minex/build'
cd /home/<...>/Development/minex/build && /usr/bin/cmake.exe -E cmake_depends "Unix Makefiles" /home/<...>/Development/minex /home/<...>/Development/minex /home/<...>/Development/minex/build /home/<...>/Development/minex/build /home/<...>/Development/minex/build/CMakeFiles/example.dir/DependInfo.cmake --color=
Dependee "/home/<...>/Development/minex/build/CMakeFiles/example.dir/DependInfo.cmake" is newer than depender "/home/<...>/Development/minex/build/CMakeFiles/example.dir/depend.internal".
Dependee "/home/<...>/Development/minex/build/CMakeFiles/CMakeDirectoryInformation.cmake" is newer than depender "/home/<...>/Development/minex/build/CMakeFiles/example.dir/depend.internal".
Scanning dependencies of target example
make[2]: Leaving directory '/home/<...>/Development/minex/build'
make -f CMakeFiles/example.dir/build.make CMakeFiles/example.dir/build
make[2]: Entering directory '/home/<...>/Development/minex/build'
[ 50%] Building CXX object CMakeFiles/example.dir/main.obj
/mingw64/bin/CC.exe -std=gnu++17 -o CMakeFiles/example.dir/main.obj -c /home/<...>/Development/minex/main.cpp
[100%] Linking CXX executable example
/usr/bin/cmake.exe -E cmake_link_script CMakeFiles/example.dir/link.txt --verbose=1
/mingw64/bin/CC.exe CMakeFiles/example.dir/main.obj -o example
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.text+0x23): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.text+0x32): undefined reference to `std::ostream::operator<<(std::ostream& (*)(std::ostream&))'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.text+0x51): undefined reference to `std::ios_base::Init::~Init()'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.text+0x81): undefined reference to `std::ios_base::Init::Init()'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.rdata$.refptr._ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_[.refptr._ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_]+0x0): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.rdata$.refptr._ZSt4cout[.refptr._ZSt4cout]+0x0): undefined reference to `std::cout'
collect2.exe: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/example.dir/build.make:103: example] Error 1
make[2]: Leaving directory '/home/<...>/Development/minex/build'
make[1]: *** [CMakeFiles/Makefile2:95: CMakeFiles/example.dir/all] Error 2
make[1]: Leaving directory '/home/<...>/Development/minex/build'
make: *** [Makefile:103: all] Error 2
Solution:
I was setting CMAKE_CXX_COMPILER wrong :/. I was doing it from memory, and I just did
CMAKE_CXX_COMPILER=... cmake ..
not
cmake .. -DCMAKE_CXX_COMPILER=...
However! It's still weird that CC is used to successfully compile cpp files, but it can't link the object files.
Solution
You have these errors because you are trying to compile/link c++ program with a c compiler. For example the two undefined references you are mentioning are part of libstdc++. It is used by default when using g++ but not with CC. If you want to use CC you have to add it manually -lstdc++.
The easiest way is to compile and link c++ programs by using g++.
For some reason the /mingw64/bin/CC.exe is considered as the CXX compiler and the working detection is skipped. to avoid the skipp of the working detection you can add set(CMAKE_CXX_COMPILER_WORKS 1). to modify the compiler it self you can set CMAKE_CXX_COMPILER as explained in CMAKE_CXX_COMPILER or set CXX as explained in CXX . be careful to clean the cache.
Answered By - yflelion Answer Checked By - Marie Seifert (WPSolving Admin)