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

Answer 1

See this question has been answered but thought others interested in this topic may appreciate a cross platform example from an old plugin based application. The example works on win32 or linux, and seaches for and calls a function called 'constructor' in the dynamically loaded .so or .dll specified in the file argument. The example is in c++ but the procedures should be the same for c.

//firstly the includes
#if !defined WIN32
   #include 
   #include 
#else
   #include 
#endif

//define the plugin's constructor function type named PConst
typedef tcnplugin* (*PConst)(tcnplugin*,tcnplugin*,HANDLE);

//loads a single specified tcnplugin,allmychildren[0] = null plugin
int tcnplugin::loadplugin(char *file) {
    tcnplugin *hpi;
#if defined WIN32               //Load library windows style
    HINSTANCE hplugin=LoadLibrary(file);
    if (hplugin != NULL) {
            PConst pinconstruct = (PConst)GetProcAddress(hplugin,"construct");
#else                                   //Load it nix style
    void * hplugin=dlopen(file,RTLD_NOW);
    if (hplugin != NULL) {
            PConst pinconstruct = (PConst)dlsym(hplugin,"construct");
#endif   
            if (pinconstruct != NULL) { //Try to call constructor function in dynamically loaded file, which returns a pointer to an instance of the plugin's class
                    hpi = pinconstruct(this, this, hstdout);
            } else {
                    piprintf("Cannot find constructor export in plugin!\n");
                    return 0;
            }
    } else {
            piprintf("Cannot open plugin!\n");
#if !defined WIN32
            perror(dlerror());
#endif
            return 0;
    }
    return addchild(hpi); //add pointer to plugin's class to our list of plugins
}

Might also be mentioned that if the module who's functions you wish to call is written in c++ your must declare the function with extern "C" such as:

extern "C" pcparport * construct(tcnplugin *tcnptr,tcnplugin *parent) {
    return new pcparport(tcnptr,parent,"PCPARPORT",0,1);
}