C Programming: Help with Pointers to Functions

devinWhalen · 03-04-2005, 12:41 PM

Hello,

I am just learning C so this might be an obvious question so bare with me....

I am writing a small program, much like grep. I search the files sent in and look for a search word. Like grep I am trying to add functionaility for an ignore case search. I want to use a pointer to a function. The functions I will use will take two char pointers and return int.
Here is a snippet of my code:

Code:

int (*comp)(char *, char *);

    if(!ignore_case)
        comp = notexact;
     else
             comp = exact;
int success = search_line(next_line, find, &search_word, comp);

I haven't made notexact yet but exact is defined as:

Code:

int exact(char *string1, char *string2)
{
 return(strcmp(string1, string2));
}

Instead of returning strcmp, I figured it would be faster to send in a pointer to strcmp like so:

Code:

int (*comp)(char *, char *);
if(!ignore_case)
        comp = notexact;
     else
             comp = strcmp;   
//comp = exact;

However, when I compile this I get the following error:
warning: assignment from incompatible pointer type

Why won't this work? Isn't strcmp defined exactly as my function exact?

Thanks for any help or pointers.....no pun intended

Later

jtshaw · 03-04-2005, 12:53 PM

Here is an example that works for me:

Code:

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

int main (void)
{
        int (*comp)(const char*, const char*);
        comp = strcmp;

        printf("%d\n",comp("same","same"));
        printf("%d\n",comp("same","notsame"));
        printf("%d\n",comp("notsame","same"));
        return 0;
}

Your problem I think is your function pointer doesn't strictly resemble the strcmp function declaration ("int strcmp(const char *s1, const char *s2);");

devinWhalen · 03-04-2005, 01:00 PM

Hey,

Thanks for the help. Now it makes perfect sense! I didn't know that strcmp took const chars.

Later