example plugin

func.c

#include <stdio.h>
#include "main.h"

void some_func(){
   burger += 10;
}

main.c

#include <stdio.h>
#include <stdlib.h> // for exit()
#include <dlfcn.h>
#include "main.h"

int burger = 3;

int main(){
   void (*ptr_func)();
   void *handle;

   handle = dlopen("./libfunc.so", RTLD_NOW);
   if (!handle) {
      fprintf(stderr, "%s\n", dlerror());
      exit(1);
   }

   *(void**)(&ptr_func) = dlsym(handle, "some_func");
   if (!ptr_func){
      fprintf(stderr, "%s\n", dlerror());
      dlclose(handle);
      exit(1);
   }

   printf("before ptr_func %d\n", burger);

   ptr_func();

   printf("after %d\n", burger);

   return 0;
}

main.h

#ifndef MAIN_H__
#define MAIN_H__
extern int burger;
#endif

Makefile

all : main libfunc.so
.PHONY : all

main : main.c
        $(CC) -rdynamic $^ -o $@

libfunc.so : func.c
        $(CC) -shared -fPIC $^ -o $@

.PHONY : clean
clean :
        rm main libfunc.so