Building a simple C++ project on Windows, using CMake and clang

Question

I'm trying to get a simple 'Hello World' program to build on Windows 10, preferably using CMake and clang. I can successfully compile, link and run the same project if I use the g++ compiler from MinGW, but have problems when I try using clang++.

I have CMake, MinGW and LLVM already installed and accessible in my path:

clang++
clang++: error: no input files

cmake --version
cmake version 3.16.0-rc1

I have set up environment variables for CMake to use clang:

echo %CC%
C:\Program Files\LLVM\bin\clang.exe
echo %CXX%
C:\Program Files\LLVM\bin\clang++.exe

Now when I run cmake with my simple "Hello World" C++ project, cmake complains about not being able to use clang:

cmake -G "MinGW Makefiles" ..
-- The CXX compiler identification is Clang 9.0.0 with GNU-like command-line
-- Check for working CXX compiler: C:/Program Files/LLVM/bin/clang++.exe
-- Check for working CXX compiler: C:/Program Files/LLVM/bin/clang++.exe -- broken
CMake Error at C:/Program Files/CMake/share/cmake-3.16/Modules/CMakeTestCXXCompiler.cmake:53 (message):
  The C++ compiler

    "C:/Program Files/LLVM/bin/clang++.exe"

  is not able to compile a simple test program.

  It fails with the following output:

    Change Dir: C:/Users/pball/git/bchest/build/CMakeFiles/CMakeTmp

    Run Build Command(s):C:/mingw-w64/x86_64-8.1.0-win32-seh-rt_v6-rev0/mingw64/bin/mingw32-make.exe cmTC_838da/fast && C:/mingw-w64/x86_64-8.1.0-win32-seh-rt_v6-rev0/mingw64/bin/mingw32-make.exe -f CMakeFiles\cmTC_838da.dir\build.make CMakeFiles/cmTC_838da.dir/build
    mingw32-make.exe[1]: Entering directory 'C:/Users/pball/git/bchest/build/CMakeFiles/CMakeTmp'
    Building CXX object CMakeFiles/cmTC_838da.dir/testCXXCompiler.cxx.obj
    C:\PROGRA~1\LLVM\bin\CLANG_~1.EXE    -g -Xclang -gcodeview -O0 -D_DEBUG -D_DLL -D_MT -Xclang --dependent-lib=msvcrtd   -o CMakeFiles\cmTC_838da.dir\testCXXCompiler.cxx.obj -c C:\Users\pball\git\bchest\build\CMakeFiles\CMakeTmp\testCXXCompiler.cxx
    Linking CXX executable cmTC_838da.exe
    "C:\Program Files\CMake\bin\cmake.exe" -E cmake_link_script CMakeFiles\cmTC_838da.dir\link.txt --verbose=1
    C:\PROGRA~1\LLVM\bin\CLANG_~1.EXE -fuse-ld=lld-link -nostartfiles -nostdlib   -g -Xclang -gcodeview -O0 -D_DEBUG -D_DLL -D_MT -Xclang --dependent-lib=msvcrtd    @CMakeFiles\cmTC_838da.dir\objects1.rsp  -o cmTC_838da.exe -Xlinker /implib:cmTC_838da.lib -Xlinker /pdb:C:\Users\pball\git\bchest\build\CMakeFiles\CMakeTmp\cmTC_838da.pdb -Xlinker /version:0.0  @CMakeFiles\cmTC_838da.dir\linklibs.rsp
    lld-link: error: could not open 'kernel32.lib': no such file or directory
    lld-link: error: could not open 'user32.lib': no such file or directory
    lld-link: error: could not open 'gdi32.lib': no such file or directory
    lld-link: error: could not open 'winspool.lib': no such file or directory
    lld-link: error: could not open 'shell32.lib': no such file or directory
    lld-link: error: could not open 'ole32.lib': no such file or directory
    lld-link: error: could not open 'oleaut32.lib': no such file or directory
    lld-link: error: could not open 'uuid.lib': no such file or directory
    lld-link: error: could not open 'comdlg32.lib': no such file or directory
    lld-link: error: could not open 'advapi32.lib': no such file or directory
    lld-link: error: could not open 'oldnames.lib': no such file or directory
    lld-link: error: could not open 'msvcrtd.lib': no such file or directory
    CLANG_~1: error: linker command failed with exit code 1 (use -v to see invocation)
    mingw32-make.exe[1]: *** [CMakeFiles\cmTC_838da.dir\build.make:88: cmTC_838da.exe] Error 1
    mingw32-make.exe[1]: Leaving directory 'C:/Users/pball/git/bchest/build/CMakeFiles/CMakeTmp'
    mingw32-make.exe: *** [Makefile:120: cmTC_838da/fast] Error 2

This is a freshly installed Windows 10 PC. It has no Visual Studio nor any Microsoft development tool installed on it. If possible I would prefer not having to install the Visual Studio for example to get the msvcrtd.lib. I am using VS Code at the moment, but this should be independent of the IDE being used.

My question is, what exactly do I have to install apart from LLVM, CMake and MinGW to make my first simple C++ project to build?

Answer 1

Don't. For the sake of your mental sanity, just build with MSVC.

Answer 2

The solution I used to compile C/C++ program with Clang compiler on Windows with CMake with whatever CMake generator is by setting the following CMake variables: (extract from a CMakePresets.json)

    "CMAKE_C_COMPILER": "clang",
    "CMAKE_CXX_COMPILER": "clang++",
    "CMAKE_C_FLAGS": "-target x86_64-pc-windows-gnu",
    "CMAKE_CXX_FLAGS": "-target x86_64-pc-windows-gnu"

Source: Clang on windows

Answer 3

To force Clang to use its own libraries instead of MSVC's, add "-target x86_64-w64-mingw32" to CMAKE_C(XX)_FLAGS.

Beware: you have to do this before CMake identifies the compiler, e.g. either before the first C or C++ project definition in CMake (e.g. before the project() call):

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -target x86_64-w64-mingw32")
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -target x86_64-w64-mingw32")

project(MyProject ...)

Alternatively, you can pass it with "-D" to CMake on the command line.

Tested with clang 10.0

Answer 4

You are missing the libraries in the linker flag. These libraries may be found in the following location:

C:\Program Files (x86)\Windows Kits\10\Lib\10.0.17134.0\um\x86

The exact path on your system may vary depending on the OS version etc., but you get the idea i believe. After finding the location you can add the path to the compiler flag in the CMakeLists.txt file e.g.,

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Xlinker /libpath:path_to_library")

See related answers:

https://software.intel.com/en-us/forums/intel-fortran-compiler/topic/784047

https://stackoverflow.com/a/48576249/811335

How /libpath flag is used:

https://learn.microsoft.com/en-us/cpp/build/reference/libpath-additional-libpath?view=vs-2019

Answer 5

Your Clang compiler is probably built to target the MSVC ABI. If I try your scenario, this is my error message:

-- The CXX compiler identification is Clang 9.0.0 
CMake Error at C:/Program Files/CMake/share/cmake-3.13/Modules/CMakeDetermineCompilerId.cmake:802 (message):   The Clang compiler tool

    "C:/Program Files/LLVM/bin/clang++"

  targets the MSVC ABI but has a GNU-like command-line interface.  This is   not supported.  Use 'clang-cl' instead, e.g.  by setting 'CXX=clang-cl' in   the environment.  Furthermore, use the MSVC command-line environment.

This was with CMake 3.13 and LLVM 9.0, and trying to use -G "MinGW Makefiles". It works using this:

SET CXX="C:/Program Files/LLVM/bin/clang-cl.exe"
cmake -G "NMake Makefiles" ..

You probably don't need to install Visual Studio, but if you want to use nmake and the MSVC libraries, you definitely need the Windows 10 SDK which is a big download, and it will be installed as well if you decide to install Visual Studio.

On the other hand, The problem seems to be related to the CMake 3.16 version. The above unsucessful tests were made with cmake 3.13, but after that I've upgraded to CMake 3.15.5 and it works perfectly. Here are the exact versions:

> cmake -version
cmake version 3.15.5
> clang++  --version
clang version 9.0.0 (tags/RELEASE_900/final)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Program Files\LLVM\bin

My build.cmd script:

SET CXX="C:/Program Files/LLVM/bin/clang++.exe"
cmake -G "MinGW Makefiles" ..

So the problem may be with your CMake version, or the MinGW libraries, as your error message is suggesting.

Answer 6

If I remember correctly, Clang attempts to use MSVC's standard library on Windows by default, since Clang's own standard library doesn't work on Windows yet.

If you don't have MSVC installed, this causes problems.

The easiest solution is to install MSYS2 and use MSYS2's patched Clang, which uses GCC's libraries by default. As a nice bonus, MSYS2 also comes with an up-to-date GCC version.

---

Alternatively, you can use -target flag to tell Clang to use GCC's libraries. If I remember correctly, this is done by adding -target x86_64-w64-mingw32 to both compiler and linker flags.

(If it doesn't work, try -target x86_64-w64-windows-gnu, I can't remember which one it is. Replace x86_64 with i686 if you're using a 32-bit compiler.)