Odtnhj

In CMake, we can add_library(mylib file1.cpp file2.cpp) and have a mylib.a in the library path get built. We can also target_include_directories(mylib INTERFACE some/directory), which effects targets depending on mylib.

But what if I have a library to begin with, which I will not be compiling. How can I add a target relating to it? That what I add as a dependency, will cause the .a file to be linked against, and for which I can set target_include_directories() ?

Note: I'm asking about CMake 3.x.

CMake provide an alternate signature for libraries that are already compiled:

add_library(
 mynamespace::mylib 
 STATIC # or it could be SHARED
 IMPORTED
)

See the official CMake documentation for more details.

with that you'll be able to add properties to the target doing so

set_target_properties(
 mynamespace::mylib
 PROPERTIES 
 IMPORTED_LOCATION "path/to/libmylib.a"
)

Little precision here, if you're using a Windows DLL, you must pass the DLL file's path in IMPORTED_LOCATION and set another property IMPORTED_IMPLIB that points to the .lib file, (not very handy).

Note that there is also a equivalent properties per configuration (Debug, and Release), that will need another property to be set (IMPORTED_CONFIGURATION), e.g. IMPORTED_LOCATION_DEBUG.

See also here and here in the documentation.

To avoid missing include files you can also precise the include directory using INTERFACE_INCLUDE_DIRECTORY property

set_target_properties(
 mynamespace::mylib 
 PROPERTIES
 INTERFACE_INCLUDE_DIRECTORIES "path/to/mylib/include"
)

With this, upon link declaration using target_link_libraries(), CMake will read information of the imported target and will add include directories implicitly.

Official documentation reference.