How to correctly add path to libfiles? - cmake

Question

My project has a dependency library in ~/SimGrid/lib directory.
How can I correctly add it to my CMakeLists.txt?
Now I try link_directories(/home/whoami/SimGrid/lib), but it doesn't help and gives:
[ 5%] Linking CXX executable CSim2Sim
/usr/bin/ld: cannot find -lsimgrid
collect2: error: ld returned 1 exit status
My full CMakeLists.txt is here:
project(CSim2Sim)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -g -O0")
set(SOURCE_FILES src/main.cpp)
add_executable(CSim2Sim ${SOURCE_FILES})
include_directories(/home/whoami/SimGrid/include)
link_directories(/home/whoami/SimGrid/lib)
target_link_libraries(CSim2Sim simgrid)

Answer 1

On Linux, linker expects library filename to be prefixed with "lib":
/home/whoami/SimGrid/lib/libsimgrid.so
If your library file has no such prefix, it cannot be found by the linker using plain library name.
As opposite, specifying full library filename in target_link_libraries call works always:
# Assume filename of the library is 'simgrid.so'
target_link_libraries(CSim2Sim /home/whoami/SimGrid/lib/simgrid.so)
In that case link_directories() call isn't needed.

Answer 2

link_directories only tells CMake what directories to look inside for the libraries you want to link to, not what libraries you want to link. My suggestion would be to create a file named SimGrid.cmake and add the following:
# -*- cmake -*-
set(SIMGRID_INCLUDE_DIRS
${CMAKE_SOURCE_DIR}/SimGrid/include
)
set(SIMGRID_LIBRARIES
simgrid.a
simgrid2.a # etc for the names of the actual libs you want to link
)
In your CMakeLists.txt add include(SimGrid) to pull the new file in.
Then in your CmakeLists.txt use the new variables and target_link_libraries which is the function you use to tell the linker what libraries you want to link:
include_directories(${SIMGRID_INCLUDE_DIRS})
target_link_libraries(CSim2Sim ${SIMGRID_LIBRARIES})
Of course, you could just add it all to your single CMakeLists.txt, but dividing it up is good practice to keep things manageable.
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -g -O0")
set(SOURCE_FILES src/main.cpp)
add_executable(CSim2Sim ${SOURCE_FILES})
link_directories(${CMAKE_SOURCE_DIR}/SimGrid/lib)
include_directories(${CMAKE_SOURCE_DIR}/SimGrid/include)
set(SIMGRID_LIBRARIES
simgrid.a
simgrid2.a
)
target_link_libraries(CSim2Sim ${SIMGRID_LIBRARIES})

Answer 3

My recommendation is to find the libs your project depends on and link it to the target. Thus any absolut or relative path are not in the cmake file but detected while run of cmake.
See How can I find a library name of .so file?