CMake: Link a library to library

Question

I have a problem with cmake. I have, lets say, CMakeLists1 which has a subdirectory where CMakeLists2 is.

In CMakeLists2 my target is a static library. And I want to link it to external library. I've made it just like that:

link_directories ("path_to_library") add_library (project2 ${sources}) target_link_libraries (project2 "name_of_external_lib") 

Then, I want to use a class from this project2 in my project1. I've made it that way:

add_executable (project1 ${sources}) target_link_libraries (project1 project2) 

But that doesn't work at all. First of all, project2 didn't link to external library. Just for checking, I've added this library through vs10 project properties, and the sizes were different. And the second thing, somehow project1 sees that external library (it is in library dependencies of this project) and of course can't find it.

What is the problem?

Answer 1

I think it's CMake's default behavior to not link project2 to the external library, but to link both libraries to the executable. From the book "Mastering CMake".

Since static libraries do not link to the libraries on which they depend, it is important for CMake to keep track of the libraries so they can be specified on the link line of the executable being created.

You could try to use an absolute path in your CMakeLists2:

add_library (project2 ${sources}) target_link_libraries (project2 "path to ext lib"/"name of ext lib") 

or you could add

link_directories ("path_to_library") 

to the CMakeLists file of project1.

If you really want to do something like in Visual Studio, you could probably use the command given in this answer to build a custom_command in CMake. It probably would look something like this (I didn't test it).

set(EXT_LIB "path_to_library/name_of_external_lib")  set(BIG_LIB "path_to_big_lib/name_of_big_lib") add_library (project2 ${sources}) get_property(PROJ2_LOC TARGET project2 PROPERTY LOCATION)  add_custom_command(OUTPUT ${BIG_LIB}                     DEPENDS ${EXT_LIB} project2                    COMMAND "lib.exe /OUT:${BIG_LIB} ${EXT_LIB} ${PROJ2_LOC} ) 

Then you could link your executable with ${BIG_LIB}.

Some things you have to consider:

• Maybe you have to use LOCATION_CONFIG (CMake docs, I found the get_property command in this answer )
• link.exe has to be in your path
• watch the scope of the BIG_LIB variable if you want to use it in an other CMakeLists.txt