Adding Features#
There are lots of compiler and linker settings. When you need to add something special, you could check first to see if CMake supports it; if it does, you can avoid explicitly tying yourself to a compiler version. And, better yet, you explain what you mean in your CMakeLists, rather than spewing flags.
The first and most common feature was C++ standards support, which got it’s own chapter.
Position independent code#
This is best known as the -fPIC
flag. Much of the time, you don’t need to do anything. CMake will include the flag for SHARED
or MODULE
libraries. If you do explicitly need it:
set(CMAKE_POSITION_INDEPENDENT_CODE ON)
will do it globally, or:
set_target_properties(lib1 PROPERTIES POSITION_INDEPENDENT_CODE ON)
to explicitly turn it ON
(or OFF
) for a target.
Little libraries#
If you need to link to the dl
library, with -ldl
on Linux, just use the built-in CMake variable ${CMAKE_DL_LIBS}
in a target_link_libraries
command. No module or find_package
needed. (This adds whatever is needed to get dlopen
and dlclose
)
Unfortunately, the math library is not so lucky. If you need to explicitly link to it, you can always do target_link_libraries(MyTarget PUBLIC m)
, but it might be better to use CMake’s generic find_library
:
find_library(MATH_LIBRARY m)
if(MATH_LIBRARY)
target_link_libraries(MyTarget PUBLIC ${MATH_LIBRARY})
endif()
You can pretty easily find Find*.cmake
’s for this and other libraries that you need with a quick search; most major packages have a helper library of CMake modules. See the chapter on existing package inclusion for more.
Interprocedural optimization#
INTERPROCEDURAL_OPTIMIZATION
, best known as link time optimization and the -flto
flag, is available on very recent versions of CMake. You can turn this on with CMAKE_INTERPROCEDURAL_OPTIMIZATION
(CMake 3.9+ only) or the INTERPROCEDURAL_OPTIMIZATION
property on targets. Support for GCC and Clang was added in CMake 3.8. If you set cmake_minimum_required(VERSION 3.9)
or better (see CMP0069, setting this to ON
on a target is an error if the compiler doesn’t support it. You can use check_ipo_supported(), from the built-in CheckIPOSupported module, to see if support is available before hand. An example of 3.9 style usage:
include(CheckIPOSupported)
check_ipo_supported(RESULT result)
if(result)
set_target_properties(foo PROPERTIES INTERPROCEDURAL_OPTIMIZATION TRUE)
endif()