pkg-config

pkg-config is a useful tool for compiling.
It helps to insert correct compiler options on the command line for gcc/g++ compiler.
example:

            `pkg-config gtk+-2.0 --cflags`                      //include gtk+2.0 lib
            `pkg-config opencv --libs --cflags opencv`    //include opencv lib

[Reference]
pkg-config wiki - http://pkg-config.freedesktop.org/wiki/