Linux Shared Libraries c++

Question

Hi all.

I have a Shared Library wise.so. How I can use it in my programm? Do I need to include headers of that library?

I work with Eclipce under Linux. I have set a path to the library using -L and -l. But my function is not visible in the program.

Could you explain me how does Shared Library work?

Regards.

EDIT:

I get the following error:

int main() {
    char* path = "/export/home/pdmazubi3/workspace/proj1/src/pic.jpg";
    CEDD_Descriptor::CEDD ced; // undefined reference to `CEDD_Descriptor::CEDD::CEDD[in-charge]()'
    ced.execute(path);
}

Header:

class CEDD
    {
     public:
      CEDD(double Th0, double Th1, double Th2, double Th3,bool CompactDescriptor);
      CEDD();
      ~CEDD(void);

      double T0;
      double T1;
      double T2;
      double T3;
      bool Compact;

      double* execute(char* path);

     private:
      int cedd_segnum;    //number of segments
      int* cedd_partitionSize;  //number of pixels in each segment
    };

Answer 1

You need to include the header file in your application and link against it.

Have a look at how to use libraries in shared libraries and Linux howto.

If the header file is not in the same directory as your application (which it usually isn't) then you need to tell compiler where to look for it, you use -I/path/to/include to include path to include directory that contains the header file.

In linking step you need to point to the library. The general usage is to use -L/path/to/lib is path to directory containing your library followed by -l<libname> where <libname> is the name of library without lib e.g. if you have libboost_serialization-d-1_34_1.so you would use -lboost_serialization-d-1_34_1

Examples:

g++ -I/sw/include -Wall -g -I/usr/local/include/boost-1_36/ -c main.cpp -o main.o
g++ -L/sw/lib -lboost_serialization-d-1_34_1 -o x main.o

Answer 2

Have you also modified the Include path (the -I option) so it knows where to look for the headers for the library? If you haven't done this then the compiler will complain about being unable to find functions/classes/structures/etc.