CMake, shared library linking fail - cmake

Question

I'm currently getting used to cmake and I'm trying to compile a small project with a .so library linking.
My project is the following.
/
CMakeLists.txt
inc/
Als.h
src/
main.c
CMakeLists.txt
lib/
libals.so
build/
I'm compiling from the build directory with:
$ cmake ..
-- DIR:
-- Configuring done
-- Generating done
-- Build files have been written to: /home/julien/tmp/cmakeTest/build
And then:
$ make
Linking C executable cmakeTest
/usr/bin/ld: ne peut trouver -lals
collect2: error: ld returned 1 exit status
src/CMakeFiles/cmakeTest.dir/build.make:85: recipe for target 'src/cmakeTest' failed
make[2]: *** [src/cmakeTest] Error 1
CMakeFiles/Makefile2:75: recipe for target 'src/CMakeFiles/cmakeTest.dir/all' failed
make[1]: *** [src/CMakeFiles/cmakeTest.dir/all] Error 2
Makefile:76: recipe for target 'all' failed
make: *** [all] Error 2
The linker seems to be unable to find the libals.so file.
Here is the file /CMakeLists.txt:
cmake_minimum_required(VERSION 2.8)
PROJECT(cmaketest)
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall")
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Werror")
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -O3")
INCLUDE_DIRECTORIES(
inc
)
ADD_SUBDIRECTORY(src)
get_directory_property(OUT_VAR LINK_DIRECTORIES)
message(STATUS "DIR: ${OUT_VAR}")
And here is the file /src/CMakeLists.txt:
PROJECT(cmakeTest)
FILE(
GLOB
${PROJECT_NAME}_Sources
*.c
)
INCLUDE_DIRECTORIES(
inc
inc
)
ADD_EXECUTABLE(
${PROJECT_NAME}
${${PROJECT_NAME}_Sources}
)
LINK_DIRECTORIES(
/home/julien/tmp/cmakeTest/lib/
)
TARGET_LINK_LIBRARIES(
${PROJECT_NAME}
als
pthread
)
Maybe I missed something but if I change the /src/CMakeLists.txt to:
PROJECT(cmakeTest)
FILE(
GLOB
${PROJECT_NAME}_Sources
*.c
)
INCLUDE_DIRECTORIES(
inc
inc
)
ADD_EXECUTABLE(
${PROJECT_NAME}
${${PROJECT_NAME}_Sources}
)
TARGET_LINK_LIBRARIES(
${PROJECT_NAME}
/home/julien/tmp/cmakeTest/lib/libals.so
pthread
)
The compilation is ok. Does someone know why the linker is unable to find libals.so when I'm giving him the good directory path to look in?
The LINK_DIRECTORIES functions seems not to be working.

Answer 1

Besides the solution you already have, and my solution in a comment, the problem you have with the CMake file shown is the order in which you invoke the CMake commands.
From the link_directories command reference:
The command will apply only to targets created after it is called.
[Emphasis mine]
You simply need to call link_directories before you call add_executable.