CODEWITHSUNDEEP
cmake
edelangh
edelangh

Reputation: 341

How to get target_link_libraries throw miss or errors

I'm using "modern cmake" with packages and would like to get errors when target_link_libraries is missing a library.

I have one CMakeLists.txt

add_library(libB
    sourceB.cpp
)
target_link_libraries(libB
    PRIVATE libC
)

and this one in an other directory

add_library(libC
    sourceC.cpp
)

target_include_directories(libC
    PUBLIC include # Will provide include/sourceC.h
)

In sourceB.cpp, I'm including sourceC.h

Here I forget to add the add_subdirectory to libC so when I build, I get this error:

sourceB.cpp:2:10: fatal error: sourceC.h: No such file or directory

How instead of this compile time error, can I ask cmake to throw me a miss error because I specifically ask to link with libC but never gave him libC ?

I saw add_dependencies but don't necessarily want libC to be built before libB

Thanks

Upvotes: 1

Views: 627

Answers (1)

KamilCuk
KamilCuk

Reputation: 141930

A simple solution is to check if it's a target. Probably somewhere on the end of your file, at least after add_subdirectory(libC)

if(NOT TARGET libC)
  message(FATAL_ERROR "Och nuu, libC is not a target")
endif()

A great solution would be to implement a target_link_targets functionality, which would allow linking only with targets. While sounds trivial, it's not so easy - static libraries can be linked circular and can be before they are defined. So you have to check if all are targets on the end of CMake file after we know every target is defined.

I did such implementation, my implementation is available here. The function k_target_link_targets checks if all arguments are targets. From CMake 3.19.0 it uses cmake_language(DEFER to defer execution of a checking function to the end of CMake scripts, before 3.19.0 a manual call to k_target_link_targets_check function is needed on the end of a CMake file.

Upvotes: 2

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