How do I load a shared object in C++?

There are two ways of loading shared objects in C++

For either of these methods you would always need the header file for the object you want to use. The header will contain the definitions of the classes or objects you want to use in your code.

Statically:

#include "blah.h"
int main()
{
  ClassFromBlah a;
  a.DoSomething();
}

gcc yourfile.cpp -lblah

Dynamically (In Linux):

#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
int main(int argc, char **argv) {
    void *handle;
    double (*cosine)(double);
    char *error;
    handle = dlopen ("libm.so", RTLD_LAZY);
    if (!handle) {
        fprintf (stderr, "%s\n", dlerror());
        exit(1);
    }
    dlerror();    /* Clear any existing error */
    cosine = dlsym(handle, "cos");
    if ((error = dlerror()) != NULL)  {
        fprintf (stderr, "%s\n", error);
        exit(1);
    }
    printf ("%f\n", (*cosine)(2.0));
    dlclose(handle);
    return 0;
}

*Stolen from dlopen Linux man page
The process under windows or any other platform is the same, just replace dlopen with the platforms version of dynamic symbol searching.

For the dynamic method to work, all symbols you want to import/export must have extern’d C linkage.

There are some words Here about when to use static and when to use dynamic linking.