Opencv_contrib: error building ```opencv_contrib/modules/tracking/include/opencv2/tracking/tracker.hpp```

[epifanio]

[ 98%] Built target opencv_test_matlab
[ 98%] Building CXX object modules/python2/CMakeFiles/opencv_python2.dir/__/src2/cv2.cpp.o
In file included from /home/epinux/dev/opencv_contrib/modules/tracking/include/opencv2/tracking/tracker.hpp:48:0,
                 from /home/epinux/dev/opencv/build2/modules/python2/pyopencv_generated_include.h:50,
                 from /home/epinux/dev/opencv/modules/python/src2/cv2.cpp:12:
/home/epinux/dev/opencv_contrib/modules/tracking/include/opencv2/tracking/onlineMIL.hpp:57:23: error: expected unqualified-id before ‘>’ token
 #define  sign(s)  ((s > 0 ) ? 1 : ((s<0) ? -1 : 0))
                       ^
/home/epinux/dev/opencv_contrib/modules/tracking/include/opencv2/tracking/onlineMIL.hpp:57:23: error: expected ‘)’ before ‘>’ token
/home/epinux/dev/opencv_contrib/modules/tracking/include/opencv2/tracking/onlineMIL.hpp:57:23: error: expected ‘)’ before ‘>’ token
modules/python2/CMakeFiles/opencv_python2.dir/build.make:296: recipe for target 'modules/python2/CMakeFiles/opencv_python2.dir/__/src2/cv2.cpp.o' failed
make[2]: *** [modules/python2/CMakeFiles/opencv_python2.dir/__/src2/cv2.cpp.o] Error 1
CMakeFiles/Makefile2:13133: recipe for target 'modules/python2/CMakeFiles/opencv_python2.dir/all' failed
make[1]: *** [modules/python2/CMakeFiles/opencv_python2.dir/all] Error 2
Makefile:160: recipe for target 'all' failed
make: *** [all] Error 2
epinux@Debian-70-wheezy-64-minimal:~/dev/opencv/build2$ 

[epifanio]

The error above is from a src build on a debian sid 64bit linux, using git master for both ospencv and opencv_contrib

[rexroni]

Found the problem, it is a macro re-definition issue. There are three places where #define sign(...) occurs. The first two are from the main opencv repo:

opencv/modules/core/test/test_eigen.cpp:#define sign(a) a > 0 ? 1 : a == 0 ? 0 : -1
opencv/modules/core/test/test_countnonzero.cpp:#define sign(a) a > 0 ? 1 : a == 0 ? 0 : -1

The last is from the opencv_contrib repo:

opencv_contrib/modules/tracking/include/opencv2/tracking/onlineMIL.hpp:#define  sign(s)  ((s > 0 ) ? 1 : ((s<0) ? -1 : 0))

The reason that the error is so cryptic is because the preprocessor is apparently expanding the sign(s) in the definition #define sign(s)..., leading to obvious problems

What I did to fix my build was to change the #define sign(s) ... to the abbreviated version #define sgn(s)..., which required two lines to be changed from a sign() call to a sgn() call in opencv_contrib/modules/tracking/src/onlineMIL.cpp. The two changes were on lines 310, and 339.

I am not sure if there is a more appropriate way to do it, but I was not able to find a way to test for the definition of a function-like macro (so as to avoid re-defining it). Perhaps, if the macro is only called twice, it may be done away with and just be manually expanded in the code.

[alalek]

Thanks for investigation!

This definition should go away from public header file and moved into .cpp file directly.

The correct form of macro is (put arg into brackets):

#define  CV_SIGN(s)  (((s) > 0) ? 1 : (((s)<0) ? -1 : 0))

or use something like this:

namespace {
    template<typename T>
    CV_INLINE int sign(const T v) {
        return (v > 0) ? 1 : ((v < 0) ? -1 : 0);
    }
} // anon namespace

[rexroni]

Happy to help! Thank you for the explanation, by the way.