Understanding writing a CMakeLists.txt [duplicate] - c++

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CMake link to external library
(6 answers)
Closed 2 years ago.
I have the following code that works perfectly with gcc by running the command:
gcc -L ~/Installed/C_LIBS/cmocka/lib -I ~/Installed/C_LIBS/cmocka/include hello.c -lcmocka -o hello
When I try to convert that to a CMakeLists.txt it breaks after running cd build && cmake .. && make with the following error codes:
Scanning dependencies of target hello
[ 50%] Building C object CMakeFiles/hello.dir/main.c.o
[100%] Linking C executable hello
ld: library not found for -lcmocka
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [hello] Error 1
make[1]: *** [CMakeFiles/hello.dir/all] Error 2
make: *** [all] Error 2
I have the code setup like this:
my-proj/
- CMakeLists.txt
- main.c
- build/
Here are my files:
main.c
#include <stdarg.h>
#include <stddef.h>
#include <setjmp.h>
#include <cmocka.h>
/* A test case that does nothing and succeeds. */
static void null_test_success(void **state) {
(void) state; /* unused */
}
int main(void) {
const struct CMUnitTest tests[] = {
cmocka_unit_test(null_test_success),
};
return cmocka_run_group_tests(tests, NULL, NULL);
}
CMakeLists.txt
cmake_minimum_required(VERSION 2.8.9)
project (hello)
include_directories(
SYSTEM ~/Installed/C_LIBS/cmocka/lib
SYSTEM ~/Installed/C_LIBS/cmocka/include
)
add_executable(hello main.c)
target_link_libraries(hello cmocka)
Can someone please tell me what I am doing wrong here? Also maybe point me in the direction of where to learn CMake better?

Answer 1

The include_directories() command only affects header search paths (stuff that is used through #include). It has no effect on library search paths.
Since you know the full path of the library, you should just be linking directly against said full path:
target_link_libraries(hello ~/Installed/C_LIBS/cmocka/lib/libcmocka.a)
However, this is just patching your CMakeLists.txt. What you should be doing is use CMake's library functions, which will be a lot more flexible:
# Include dir
find_path(MOCKA_INCLUDE_DIR
NAMES cmocka.h
PATHS ~/Installed/C_LIBS/cmocka/include
)
#library itself
find_library(MOCKA_LIBRARY
NAMES cmocka
PATHS ~/Installed/C_LIBS/cmocka/lib
)
target_include_directories(hello PRIVATE ${MOCKA_INCLUDE_DIR})
target_link_libraries(hello ${MOCKA_LIBRARY})