Question

I read a few tutorials about loading shared libraries and call functions in them. I succeded on both points. There’s just one thing I didn’t see in any of the tutorials:

How do I return a value from a function in a shared library to the main code?

This is my shared library source:

#include <stdio.h>

char* entry(){
  printf("this is a working plugin\n");

  return "here we go!";
}

When i call it, i get “this is a working plugin” on the stdout. My question is now, how i can get the “here we go” string back to the main.c which looks like:

void *lib_handle;
void (*lib_func)();

...

lib_handle = dlopen("/home/tectu/projects/tibbers/plugins.so", RTLD_LAZY);
if(!lib_handle)
  error("coudln't load plugins", NULL);

lib_func = dlsym(lib_handle, "entry");
  if(!lib_func)
    error("coudln't find symbol in plugin library", NULL);

(*lib_func)();  // here i call the entry() from the .so

Something like this does not work:

printf("return value: %s\n, (*lib_func)());

So, any ideas?

Thank you.

Answer 1

It works when lib_func is properly declared:

char* (*lib_func)();

You might need to cast in the assignment from dlsym.