How to add include rule for other directory?

Question

I have this directory structure :

- code
  - shared lib 1
    - unit tests
  - shared lib 2
    - unit tests
- extern libs
  - gtest + gmock
  - extern lib

Each directory has one CMakeLists.txt file.

Shared library 2 needs to link shared library 2. This I solved, how to solve the include?

Here are my CMakeList.txt files for shared lib 1 :

SET( LIB_OUTPUT_NAME shlib1 )

FILE (GLOB HEADER_FILES ./*.hpp)
FILE (GLOB SOURCE_FILES ./*.cpp)

ADD_LIBRARY (${LIB_OUTPUT_NAME} SHARED ${SOURCE_FILES} ${HEADER_FILES} )

and for shared lib 2 :

SET( LIB_OUTPUT_NAME shlib2 )

# what to put here? this doesn't work
include_directories(${shlib1})

FILE( GLOB HEADER_FILES ./*.hpp )
FILE( GLOB SOURCE_FILES ./*.cpp )

ADD_LIBRARY( ${LIB_OUTPUT_NAME} SHARED ${SOURCE_FILES} ${HEADER_FILES} )

target_link_libraries( ${LIB_OUTPUT_NAME} shlib1 ) 

PS: I got more libraries - not just 2. That is why I am looking at more generic solution.

---

I tried to use target_include_directories like this :

target_include_directories( ${LIB_OUTPUT_NAME} PUBLIC ${shlib1} )

but it didn't work.

Answer 1

If you're using CMake v2.8.11 or newer, then target_include_directories is indeed the way to go.

It's not clear from your question which CMakeLists.txt you've added this command to. If you're trying to specify that any target which depends on shlib1 should have "code/shared lib 1" as an include search path, then you should add the command to "code/shared lib 1/CMakeLists.txt".

In your target_include_directories call, you're specifying that the public search path should be ${shlib1}. I expect that this variable is actually empty - you're certainly not setting it anywhere in your example code. What is available however is the variable shlib1 - this is the target created in your add_library call, but it's not too useful here.

So, your command in "code/shared lib 1/CMakeLists.txt" should be something like:

target_include_directories(${LIB_OUTPUT_NAME} PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})

If you don't want to use target_include_directories (or have to cater for older versions of CMake), you would have to use include_directories in "code/shared lib 2/CMakeLists.txt". However, you'd have to pass the path to "code/shared lib 1".

You could just use a relative path but this perhaps isn't the most robust solution:

include_directories("../shared lib 1")

or assuming you have your top-level CMakeLists.txt in "code", you could do:

include_directories("${CMAKE_SOURCE_DIR}/shared lib 1")

but this isn't much better.

A more robust option might be to make each subdirectory a separate project (i.e. have a project call at the top of each subdir's CMakeLists.txt). This makes the variable <projectName>_SOURCE_DIR available to all subsequent CMake files. So, if your first shared lib also had project(sharedlib1), then in "code/shared lib 2/CMakeLists.txt" you could do:

include_directories(${sharedlib1_SOURCE_DIR})

Or another reasonable solution would be to set a cache variable (to make it available everywhere) in every subdir's CMakeLists.txt, specifying that subdir's public search path(s). For example, in "code/shared lib 1/CMakeLists.txt":

set(shlib1_includes "${CMAKE_CURRENT_SOURCE_DIR}" CACHE INTERNAL
    "Public include path(s) for shlib1")

then in "code/shared lib 2/CMakeLists.txt":

include_directories(${shlib1_includes})