How come CHECK_FUNCTION_EXISTS
doesn't find clock_gettime
?
I use the following code in my CMakeLists.txt
:
include(CheckFunctionExists)
set(CMAKE_EXTRA_INCLUDE_FILES time.h)
CHECK_FUNCTION_EXISTS(clock_gettime HAVE_CLOCK_GETTIME)
This is on a POSIX system I know has clock_gettime
. Yet I simply get:
-- Looking for clock_gettime - not found
Because clock_gettime
is found in librt
we need to link to that when doing the check (otherwise CMake will simply fail to compile the test program it generates to test if the function exists).
This is not possible with CHECK_FUNCTION_EXISTS
. Instead CHECK_LIBRARY_EXISTS must be used:
include(CheckLibraryExists)
CHECK_LIBRARY_EXISTS(rt clock_gettime "" HAVE_CLOCK_GETTIME)
This will now work and output:
-- Looking for clock_gettime in rt - found
Update: In newer glibc 2.17+ clock_gettime
has been moved from librt
to libc
.
So to be sure to find clock_gettime
on all systems you would need to do two checks:
include(CheckLibraryExists)
CHECK_LIBRARY_EXISTS(rt clock_gettime "" HAVE_CLOCK_GETTIME)
if (NOT HAVE_CLOCK_GETTIME)
set(CMAKE_EXTRA_INCLUDE_FILES time.h)
CHECK_FUNCTION_EXISTS(clock_gettime HAVE_CLOCK_GETTIME)
SET(CMAKE_EXTRA_INCLUDE_FILES)
endif()
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