How do I specify the include directory for an imported shared library using CMake?

Question

I am using cmake version 3.9.1.

I have a third party shared library and header file in my source tree. I am trying to add it as a link target.

All the documentation I can find says that this should work:

test.cpp

#include "ftd2xx.h"

int main(int argc, char **argv)
{
    FT_HANDLE handle;
    FT_STATUS status = FT_Open(1, &handle);

    return 0;
}

CMakeLists.txt

cmake_minimum_required (VERSION 3.6)
project(test_proj CXX)
add_subdirectory(ftdi)
add_executable(mytest test.cpp)
target_link_libraries(mytest ftd2xx)

ftdi/CMakeLists.txt

add_library(ftd2xx SHARED IMPORTED)
set_target_properties(ftd2xx PROPERTIES INTERFACE_INCLUDE_DIRECTORIES ${CMAKE_CURRENT_SOURCE_DIR})
set_target_properties(ftd2xx PROPERTIES IMPORTED_LOCATION ${CMAKE_CURRENT_SOURCE_DIR})

However compiling test.cpp, which includes "ftd2xx.h", complains that it cannot find the header file and the relevant -I<path> entry is missing from the generated makefiles.

If I specify the library as INTERFACE rather than SHARED IMPORTED then the header file is found correctly, but CMake barfs on setting the IMPORTED_LOCATION property.

If I specify the library as INTERFACE rather than SHARED IMPORTED and then use target_link_libraries to point directly to the library file than this works for Windows but not for Linux.

I'd appreciate any help anyone can offer.

Answer 1

The CMake documentation does actually answer this one, but so concisely, and in the middle of a much larger paragraph, that it is easy to miss:

The target name has scope in the directory in which it is created and below, but the GLOBAL option extends visibility.

I am using the target name in a higher level directory, so I need to declare the library as SHARED IMPORTED GLOBAL rather than just SHARED IMPORTED.

Final code is:

add_library(ftd2xx SHARED IMPORTED GLOBAL)
set_target_properties(ftd2xx PROPERTIES INTERFACE_INCLUDE_DIRECTORIES ${CMAKE_CURRENT_SOURCE_DIR})

And then for Windows:

    set_target_properties(ftd2xx PROPERTIES IMPORTED_IMPLIB ${CMAKE_CURRENT_SOURCE_DIR}/win32/ftd2xx.lib)
    set_target_properties(ftd2xx PROPERTIES IMPORTED_LOCATION ${CMAKE_CURRENT_SOURCE_DIR}/win32/ftd2xx.dll)

And for Linux:

    set_target_properties(ftd2xx PROPERTIES IMPORTED_LOCATION ${CMAKE_CURRENT_SOURCE_DIR}/i386/libftd2xx.so)