How to create a cmake header-only library that depends on external header files?
I've used an empty _only_for_compiling_the_lib.cpp
file as the simplest and fastest workaround, but clearly the above solution is strongly advised.
I simply wasn't aware of INTERFACE
keyword.
As stated in the comments, target_include_directories
should be given a path to a directory, not to a file.
Moreover, if you want to create a dependency for lib2
on lib1
, you should do it through target_link_libraries
: a dependency is not only about include directories, but also about compile options, definitions, target properties...
target_sources
doesn't work with interface libraries. From this answer, You can use a custom target without commands to associate the sources to a target without impacting the build process (for msvc, QtCreator and other GUI-based tools, this makes the sources accessible through the IDE; AFAIK it's useless for other build tools).
Your cmake may look like this:
add_library(lib1 INTERFACE)
target_sources(lib1 INTERFACE lib1.h)
target_include_directories(lib1 INTERFACE
"${PROJECT_SOURCE_DIR}/lib1"
)
add_library(lib2 INTERFACE)
if(MSVC)
add_custom_target(lib2.headers SOURCES lib2.h)
endif()
target_include_directories(lib2 INTERFACE
"${PROJECT_SOURCE_DIR}/lib2"
)
target_link_libraries(lib2 INTERFACE lib1)
add_executable(project main.cc)
target_link_libraries(project lib2)
Advanced tip: you can specify a different directory in target_include_directories
for the build tree and the install tree (see documentation):
target_include_directories(lib1 INTERFACE
$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/lib1>
$<INSTALL_INTERFACE:${YOUR_INSTALL_DIR}/lib1>
)