How to find out which lib file I need to link while I use a third party library?

Question

For example if I use a function in opencv, and I can use two methods to specify the libs and link them. First one, I can use find_package(OpenCV 3.3 REQUIRED) and them target_link_libraries( main ${OpenCV_LIBS}) because the macro include all the libraries we need. Second one, I want to link my opencv without ".cmake" and I need to give CMakeLists.txt a link_directiories(/xxxx) and use target_link_libraries(main opencv_core opencv_imgcodecs).

So my question is how can I quickly find out which lib I should link while I use the second method. Like I use some function in the opencv_core.so but actually I know it by try several times among much libs in opencv.

Answer 1

There is no quick way to do it, apart maybe from reading your library documentation. In OpenCV it is quite straightforward, documentation specifies the list of the modules, then your rule of thumb should be: whenever you #include <opencv2/MODULE_NAME.hpp>, you link to opencv_MODULE_NAME. E.g. #include <opencv2/imgproc.hpp> , then you should link with opencv_imgproc.

If you don't have this kind of information beforehand, on the Linux machine you can investigate the symbols in the available dynamic libraries:

for lib in `find LIB_PATH -name "*.so"`; do echo ${lib}; nm -D -C ${lib}; done

where LIB_PATH is where your libraries are installed, e.g. /usr/lib.

You can then save the output and search for the undefined symbol that was reported by your linker while building your project. Instead of "*.so" you can have more restrictive pattern like libopencv*.so to limit the output.