Question

Using CMake I want to check if a particular function (cv::getGaborKernel) from OpenCV library is available (it is available only in quite recent version of the library). If it is, I will use it in my code, if it is not, I redefine it in my code, in btw #ifdefs.

Here is a snippet of my CMakeLists.txt:

FIND_PACKAGE(OpenCV REQUIRED)
include_directories(${OpenCV_INCLUDE_DIRS})

get_property(inc_dirs DIRECTORY PROPERTY INCLUDE_DIRECTORIES)
set(CMAKE_REQUIRED_INCLUDES ${OpenCV_INCLUDE_DIRS})
set(CMAKE_REQUIRED_LIBRARIES ${OpenCV_LIBS})
INCLUDE(CheckCXXSourceCompiles) 
CHECK_CXX_SOURCE_COMPILES(
"
#include <opencv2/imgproc/imgproc.hpp>
int
main()
{
cv::Mat toto = cv::getGaborKernel(cv::Size(11,11), 1,0,3,1,0, CV_64F);
}
" HAVE_OPENCV_GABOR)
if(HAVE_OPENCV_GABOR)
message("Using OpenCV Gabor implementation")
else(HAVE_OPENCV_GABOR)
message("Using custom Gabor implementation")
endif(HAVE_OPENCV_GABOR)

When deploying on a computer with recent OpenCV version (which does have cv::getGaborKernel), the test fails, forcing the redefinition of the function and some compilation errors.
The problem reside in the fact that OpenCV not beeing installed in standard directory, it first fails to locate the library. So the sample program cannot be built. However, after I properly set up OpenCV dependencies, the test for HAVE_OPENCV_GABOR is not run again as the failure is registered in the cache.
How can I force CMake to rerun the test in that case?

Answer 1

Just wrap your CHECK_CXX_SOURCE_COMPILES() call with

if(NOT OpenCV_INCLUDE_DIRS OR NOT OpenCV_LIBS)
...
endif()

Another solution – add unset(HAVE_OPENCV_GABOR CACHE) before running CHECK_CXX_SOURCE_COMPILES().