How can I add linker flag for libraries with CMake?

Question

When linking a binary I can use CMAKE_EXE_LINKER_FLAGS to add a flag (let's say -Wl,-as-needed). However, if I link a library this extra flag will not be taken into account. I would need something like CMAKE_LIB_LINKER_FLAGS but I can't find it.

How should I do this?

Answer 1

Note: modern CMake has a better solution than mentioned below (see updates for details).

You can use CMAKE_SHARED_LINKER_FLAGS like:

set (CMAKE_SHARED_LINKER_FLAGS "-Wl,--as-needed")

This question looks like related.

UPD
Thanks to @Bruce Adams who points out that since v3.13 CMake has special command for such purpose: add_link_options.

UPD 2
Thanks to @Alex Reinking who points out that modern CMake doesn't recommend using global settings. It is suggested to give the preference to the property settings before the global ones, so instead of add_link_options that has a global scope, the target_link_options should be used. See Alex's answer for details.

Answer 2

This is how you add linker flags to a target in modern CMake (3.13+):

# my_tgt can be an executable, library, or module.
target_link_options(my_tgt PRIVATE "LINKER:-as-needed")

Note that CMake always passes flags to the configured compiler. Thus, to forward your intended link flags to the linker, you must use the LINKER: prefix. CMake will take care of expanding it to -Wl,-as-needed on GCC, and to -Xlinker -as-needed on Clang.

See the documentation here: https://cmake.org/cmake/help/latest/command/target_link_options.html

Answer 3

It looks like this problem is related to the one I had in CLION. I solved it by adding

{set(CMAKE_CXX_STANDARD_LIBRARIES -ljpeg)}

to CMakeLists.txt.