Creating a module system (dynamic loading) in C

Question

How would one go about loading compiled C code at run time, and then calling functions within it? Not like simply calling exec().

EDIT: The the program loading the module is in C.

Answer 1

dlopen is the way to go. Here are a few examples:

Loading a plugin with dlopen:

#include <dlfcn.h> ... int main (const int argc, const char *argv[]) {    char *plugin_name;   char file_name[80];   void *plugin;   ...   plugin = dlopen(file_name, RTLD_NOW);   if (!plugin)   {      fatal("Cannot load %s: %s", plugin_name, dlerror ());   } 

Compiling the above:

% cc  -ldl -o program program.o  

Then, assuming this API for the plugins:

/* The functions we will find in the plugin */ typedef void (*init_f) (); init_f init; typedef int (*query_f) (); query_f query; 

Finding the address of init() in the plugin:

init = dlsym(plugin, "init"); result = dlerror(); if (result) {    fatal("Cannot find init in %s: %s", plugin_name, result); } init(); 

With the other function, query(), which returns a value:

query = dlsym (plugin, "query"); result = dlerror(); if (result) {     fatal("Cannot find query in %s: %s", plugin_name, result); } printf("Result of plugin %s is %d\n", plugin_name, query ()); 

You can retrieve the complete example on line.