[SOLVED] Function pointers with variable arguments

kvm1983 · 07-14-2011, 08:49 PM

I need to call functions that match an input string (if input str = "func1", call func1), so I have this:

Code:

#include <stdio.h>
#include <string.h>

void function_a(void) { printf("Function A\n"); }
void function_b(void) { printf("Function B\n"); }
void function_c(void) { printf("Function C\n"); }
void function_d(void) { printf("Function D\n"); }
void function_e(void) { printf("Function E\n"); }

const static struct {
    const char *name;
    void (*func)(void);
} function_map [] = { 
    { "function_a", function_a },
    { "function_b", function_b },
    { "function_c", function_c },
    { "function_d", function_d },
    { "function_e", function_e },
};

int call_function(const char *name)
{
    int i;

    for (i = 0; i < (sizeof(function_map) / sizeof(function_map[0])); i++) {
        if (!strcmp(function_map[i].name, name) && function_map[i].func) {
            function_map[i].func();
            return 0;
        }   
    }   

    return -1; 
}

int main()
{
    call_function("function_a");
    call_function("function_c");
    call_function("function_e");
}

In the above example, the functions take no input arguments. Can they take a different number of arguments, for example, function_a(int), function_c(int, int), function_e(int, char, int)? How can I do that?

Thanks,
Kshitij

kvm1983 · 07-14-2011, 09:05 PM

I think I HAVE to do something like this:

if( strcmp(funcname, "function_a") == 0)
function_a(int);
else if ( strcmp(funcname, "function_b") == 0)
function_b(int, int);

I was looking for a more graceful way of doing it, but I dont think there is. Maybe I asked the question prematurely.

flamelord · 07-14-2011, 09:24 PM

Yes, it is possible. If I understand what you are asking, then you would have something like:

Code:

#include <stdargs.h>

/*
...
*/

int call_function(const char *name, ...)
{
    int i;
    va_list argp;

    va_start(argp, name);

    for (i = 0; i < (sizeof(function_map) / sizeof(function_map[0])); i++) {
        if (!strcmp(function_map[i].name, name) && function_map[i].func) {
            function_map[i].func(argp);
            va_end();
            return 0;
        }   
    } 
    
    va_end();  

    return -1; 
}

And then your functions will need to be of the form

Code:

void function_x(va_list args);

And within the function you will need to extract the arguments using va_arg(args,<type>).

What I have given you is only a rough outline, but it gives you the general idea. You may also want to look at http://c-faq.com/~scs/cclass/int/sx11b.html

kvm1983 · 07-14-2011, 10:12 PM

Thank you very much. That helped.