Thread: question about functions and char *

Hello all,

I'm having trouble with my code, hoping someone will be able to help.

I'm trying to pass an argument to a function, have it look up an entry in a linked list, and return the corresponding entry. The problem is that when I return the pointer, it doesn't print out correctly in the calling function. Here's the two functions:

calling function:

Code:

void do_something(char * src_ip, char * des_ip) {
...
char * src_i_face;
char * des_i_face;

src_i_face = get_iface(src_ip);
des_i_face = get_iface(des_ip);
...
free(src_i_face);
free(des_i_face);
...

and here is the get_iface method:

Code:

char * get_iface(char * ip)
{
// pointer to top of global list
// int_list is a global linked list
struct bgp_cef * temp = int_list;
char * i_face;
char * parsed_ip;
char * test_ip;

       // another method that does parsing
        parsed_ip = parse_ip(ip);

        i_face = (char *)malloc(50 * (sizeof(char)));

        while (int_list != NULL)
        {
                // parsing
                test_ip = parse_ip(int_list->ip);

                if(!strncmp(test_ip, parsed_ip, int_list->bits)) {
                        strcpy(i_face, int_list->interface);
                        int_list = temp;
                        free(parsed_ip);
                        free(test_ip);
                        return i_face;
                }

        int_list = int_list->next;
        }
}

obviously there's more going on in this program - but I've tried to be succinct. The problem is in the get_iface method, returning the char *.

Any help would be greatly appreciated, as I'm ready to toss my computer out the window in frustration...

um, unfortunately I don't think that's the problem...

if I try to print i_face in the method, the variable seems fine. when I try to print it in the calling function, I get a garbled mess.

I think this is a problem with the memory allocation, but I can't figure out what the problem is.

First off, thanks to both of you for your quick responses - it's much appreciated. I'm usually a Java programmer, so going back to C after not touching it since 1rst year uni has been frustrating...

I think the problem is in my printf call after calling the function. If I code:

Code:

printf("\n%s %s", str1, str2);

it appears that str1 is being overwritten on the output screen.

however, if I break it up:

Code:

printf("\n%s", str1);
printf("\n%s", str2);

... everything's fine. Anyone have any ideas why this is?

thanks again