In my project some code can be optional compiled in a different language (nasm & fortran), but it's also fine to compile the project without having these compiler installed. E.g. on Windows.
I would like to check if the the compiler are installed, before enabling the languages with enable_language
enable_language(ASM_NASM)
enable_language(Fortran)
If I use enable_language without an additional check, CMake stops with an error message.
(At the moment I check for if (MSVC) as workaround.)
Btw. I have a similar problem with the check for Qt. The check don't stop with an error, but generate a lot of noisy warnings.
So use check_language to check if a language can be enabled.
Related
I'm a *nix user, installing LLVM is easy for me, just download the precompiled file, set LLVM_DIR, and you're done. But I'm having a lot of problems with Windows ...
I downloaded LLVM-<version>-win64.exe from the GitHub release, but I can't find LLVMConfig.cmake file. Then I tried to compile LLVM from the source following this documentation.
When I started compiling my own project, I got this error:
'C:/<...>/Debug/libLLVMSupport.lib', needed by '<...>.exe', missing and no known rule to make it
I guess maybe I'm missing some compile options. but I can't find the documentation for LLVM_ENABLE_PROJECTS or BUILD_SHARED_LIBS, not even a list of component names.
I tried to add -DBUILD_SHARED_LIBS=ON but CMake told me BUILD_SHARED_LIBS option is not supported on Windows.
I am new to CMake and my IDE (CLion) has not yet supported the intellisense for add_custom_target() include source files. One of the comments in the YouTrack Issue, mentioned that a add_library(_fake) would do the trick. I tried several combinations of getting my custom target sources linked to _fake library, but it won't work for me.
I need to use clang for this target and CMake does not seem to provide a way to pick the compiler for individual targets, so I am stuck with custom_target approach. When I add the custom target sources to _fake library, it can't compile with cc.
While VSCode seem to provide intellisense for custom target, CLion fails to do so. Is there a way to not compile the _fake library to avoid compilation errors from cc and yet get the intellisense working? If not how can I get CLion intellisense working just like VSCode can do without any trick?
If you build C++14 code with G++ and libstdc++, there's a library named libstdc++fs, which is separate from the rest of libstdc++, and contains the code for std::experimental::filesystem. If you don't link against it, you'll get undefined references.
The "trick" I'm using for overcoming this right now is:
if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
set(CXX_FILESYSTEM_LIBRARIES "stdc++fs")
endif()
and later:
target_link_libraries(my_target PUBLIC ${CXX_FILESYSTEM_LIBRARIES})
but - I don't like having to place this code in every project I work on. Is there a simpler or more standard idiom I could use? Some way this will all happen implicitly perhaps, with some CMake behind-the-scences magic?
tl;dr: Nothing right now, wait for a newer CMake version
As #Pedro graciously points out, this is a known problem, and there is an open issue about it at KitWare's GitLab site for CMake:
Portable linking for C++17 std::filesystem
If using CMAKE_CXX_STANDARD=17 and std::filesystem, GCC requires linking of an extra library: stdc++fs. ... If C++17 is enabled, would it be worth automatically linking to stdc++fs for GCC versions which require this? Likewise for any quirks in other compilers or libraries.
The KitWare issue is about C++17, for which apparently you still need the separate extra library (i.e. it's not just because of the "experimentality" in C++14). Hopefully we'll see some traction on this matter - but
Note: If you're experiencing this problem with C++17's std::filesystem, you're in luck - that code is built into libstdc++ beginning with GCC 9, so if you're using g++ 9 or later, and std::filesystem, you should no longer experience this problem.
I was trying to parallelize a Fortran program using MPI. I use CMake to do the build of my program. It was difficult to find support on getting CMake to create a working makefile for Fortran with MPI support on google, but from what I could gather, I added the following commands to my CMakeLists.txt script:
find_package(MPI REQUIRED)
add_definitions(${MPI_Fortran_COMPILE_FLAGS})
include_directories(${MPI_Fortran_INCLUDE_DIRS})
link_directories(${MPI_FortranLIBRARY_DIRS})
This will locate MPI on my system and then set the variables found in the following three commands. In my linking line, I added the MPI libraries variable to the list of the other libraries that my program needed to build.
target_link_libraries(${exe_name} otherlibs ${MPI_FortranLIBRARY_DIRS})
Doing cmake and then make worked to build the program and the program ran; however, when I tried to add more to the source which required me to include the mpif.h include file, my compilation failed due to not being able to find this header file. I also could not use mpi because the compiler cannot find the mpi.mod file in the path.
I inserted "message" commands into my CMakeLists.txt file and printed out the values of the variables that I was using for including and linking. It turns out that the variables, MPI_Fortran_INCLUDE_DIRS and MPI_FortranLIBRARY_DIRS weren't set to anything. A check of the module that CMake is actually using to set these variables (FindMPI.cmake) showed these variables to be non-existent. I changed my CMakeLists.txt file to use the correct variables:
find_package(MPI REQUIRED)
add_definitions(${MPI_Fortran_COMPILE_FLAGS})
include_directories(${MPI_Fortran_INCLUDE_PATH})
link_directories(${MPI_Fortran_LIBRARIES})
target_link_libraries(${exe_name} otherlibs ${MPI_Fortran_LIBRARIES})
Now when I execute make, the compiler could find both mpif.h as well as mpi.mod.
UPDATE:
I want to mention that this solution worked for cmake version 2.8.10.1. When I moved my CMakeLists.txt scripts to a different machine that has cmake version 2.8.4, I get the same error about mpi.mod missing during the link stage. I checked the FindMPI.cmake module and, sure enough, there are no variables that specify the language (i.e. there is no MPI_Fortran_LIBRARIES variable, just a MPI_LIBRARIES variable, and this variable is not getting set to the correct location of the mpi library on that system. So this solution will be dependent on cmake version.
Sounds like you are not using the mpi compiler. That is fine, but you have to add a lot of flags then. There is not really an mpi compiler but a wrapper that sets the flags to be able to use mpi. With cmake I was able to do this by defining the fortran compiler I was going to use BEFORE the call to cmake. It's not a nice solution since you loose portability, but it works. I'm trying to find a better solution and define inside cmake what compiler to use, but have not been able to do so. In other words, this works for me:
FC=mpif90 cmake ../.
make
I was having the same problem as you. Hope this solves the issue. If anybody finds how to define the fortran compiler INSIDE cmake please post it!
as you've already noticed, you misspelled the name of two variables, namely MPI_Fortran_LIBRARIES and MPI_Fortran_LIBRARIES
It is useful also to add:
cmake_minimum_required(VERSION 2.8.10)
at the very beginning of your CMake to be sure that these variables will be defined.
Windows VC++ 2008
linux gcc 4.4.3
I have the following problem. When I compile on windows I need the ws2_32 library. However, when I compile on linux, I don't need to link this.
My CMakeLists.txt
INCLUDE_DIRECTORIES($CLIENT_SERVER_SOURCE_DIR/client)
INCLUDE_DIRECTORIES($CLIENT_SERVER_SOURCE_DIR/cltsvr_ults)
# Link the library
LINK_DIRECTORIES($CLIENT_SERVER_DIR/client)
# Add the executable
ADD_EXECUTABLE(clt test_clt)
# Link the executable to the client library
IF(WIN32)
TARGET_LINK_LIBRARIES(clt client ws2_32)
ENDIF(WIN32)
IF(CMAKE_COMPILER_IS_GNUCXXX)
TARGET_LINK_LIBRARIES(clt client)
ENDIF(CMAKE_COMPILER_IS_GNUCXXX)
I have tried unsuccessfully to compile under linux. Using the above conditions. However, It always tries to link the ws2_32 and I get a compile error. I think that the conditions aren't working, as it always falls through the WIN32 condition.
many thanks for any suggestions,
Since the WIN32 thing is such a fundamental part of CMake, I'd guess that there is more to this than what you mention.
Are you doing a clean check out of your code, or just copying up a whole directory on Linux? If you have all your CMake build files cached from the Windows build, maybe (just maybe!) something has snuck in there and "detects" itself as WIN32 on Linux?
Are you sure it is that line and not something else that causes the link to the stray Win-library? Maybe try a MESSAGE(STATUS "I am here")line within the IF(WIN32) just to make sure.
Are you sure the error is caused by linking that library? I can see a typo in your script, it should be IF(CMAKE_COMPILER_IS_GNUCXX) - you have an extra X on there. Perhaps you are not linking in what you thing you are, and that is why it fails.