CMake with clang shows undefined symbol, and with cl links correctly - c++

Question

TLDR
Im building a static library and linking it to an executable. Im generating makefiles with cmake. When I generate the makefile for cl (The compiler from visual studio) I have no problems, but when I generate the makefile for clang I get an undefined symbol.
Versions:
cmake version 3.18.1
clang version 11.0.0
Target: x86_64-pc-windows-msvc
Thread model: posix
cl version 19.26.28806 for x64
Minimal Example
I have the following structure for the proyect:
Proyect Root
│ CMakeLists.txt
│ foo.cpp
│ foo.hpp
│ main.cpp
│
└───bin
And this are the contents of the files:
foo.hpp
namespace foo {
void do_stuff(void);
}
foo.cpp
#include <foo.hpp>
namespace foo {
void do_stuff(void) {}
}
main.cpp
#include <foo.hpp>
int main(void) {
foo::do_stuff();
return 0;
}
And CMakeLists.txt
cmake_minimum_required(VERSION 3.0.0)
project(CompileAndLinkLib)
include_directories(".")
file(GLOB FOO_SRC "foo.cpp")
add_library(foo STATIC ${FOO_SRC})
add_executable(main "main.cpp")
target_link_libraries(main foo)
Correct linking
First I call vcvarsall.bat. I generate a nmake file with the following command:
cmake .. -G "NMake Makefiles"
And compile with:
nmake
The project compiles and links correctly
The undefined symbol
I generate the make file with the following command:
cmake .. -G "Unix Makefiles" -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
And when I compile with make I get the following output:
Scanning dependencies of target foo
[ 25%] Building CXX object CMakeFiles/foo.dir/foo.cpp.obj
[ 50%] Linking CXX static library foo.lib
[ 50%] Built target foo
Scanning dependencies of target main
[ 75%] Building CXX object CMakeFiles/main.dir/main.cpp.obj
[100%] Linking CXX executable main.exe
lld-link: error: undefined symbol: void __cdecl foo::do_stuff(void)
>>> referenced by C:\Users\pabsa\temp\main.cpp:4
>>> CMakeFiles/main.dir/main.cpp.obj:(main)
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [main.exe] Error 1
make[1]: *** [CMakeFiles/main.dir/all] Error 2
make: *** [all] Error 2
Im not sure if im doing something wrong, like if im missing something, or if this is an error with the makefile generated by cmake.

Answer 1

I just had the same problem, but with Clang 13. It could be solved with specifying clang as compiler in the CMakeLists, instead of letting CMake determine it automatically.
set(CMAKE_CXX_COMPILER "clang++")
(And yes, I read your original question correct, using this:
-DCMAKE_CXX_COMPILER=clang++
as an additional argument for cmake did not work for me as well, even if it looks like it should behave the same as setting it in CMakeLists.txt)

Answer 2

I tested again with:
clang version 12.0.0
Target: x86_64-pc-windows-msvc
Thread model: posix
And it worked corretly. Seems like it was a problem with clang 11

Answer 3

You're overcomplicating things imo. What about just "cmake .. -T ClangCL && cmake --build ."? Builds fine for me:
C:\Users\vital\test\_build>cmake .. -T ClangCL
-- Building for: Visual Studio 17 2022
-- Selecting Windows SDK version 10.0.20348.0 to target Windows 10.0.22000.
-- The C compiler identification is Clang 14.0.5 with MSVC-like command-line
-- The CXX compiler identification is Clang 14.0.5 with MSVC-like command-line
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: C:/Program Files/Microsoft Visual Studio/2022/Community/VC/Tools/Llvm/x64/bin/clang-cl.exe - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: C:/Program Files/Microsoft Visual Studio/2022/Community/VC/Tools/Llvm/x64/bin/clang-cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: C:/Users/vital/test/_build
C:\Users\vital\test\_build>cmake --build .
MSBuild version 17.3.1+2badb37d1 for .NET Framework
Checking Build System
Building Custom Rule C:/Users/vital/test/CMakeLists.txt
foo.vcxproj -> C:\Users\vital\test\_build\Debug\foo.lib
Building Custom Rule C:/Users/vital/test/CMakeLists.txt
main.vcxproj -> C:\Users\vital\test\_build\Debug\main.exe
Building Custom Rule C:/Users/vital/test/CMakeLists.txt
C:\Users\vital\test\_build>