Functions in C counting an array of characters

Question

I am trying to write a small program where I basically count the string length in a function but for some reason it is not outputting anything to the command line.

#include <stdio.h>

int search (char* string, char* substring){
    int length = 0;
    while(substring){
        substring++;
        length++;
    }
    return length;

}


int main(int argc, const char * argv[])
{
    char string1[] = "hello world";
    char* string = string1;
    char substring1[] = "world";
    char* substring = substring1;

    int a = search(string,substring);

    printf("%d", a);
    return 0;
}

cnicutar · Accepted Answer · 2013-02-07 23:14:53Z

4

You need to dereference it or you'll keep looping since there's no obvious way for substring to become 0.

while (*substring)
       ^

That's because you're not looking for the NULL pointer but rather for the NUL (\0) character.

answered Feb 7, 2013 at 23:14

cnicutar

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1 Comment

user1334858 Over a year ago

So simple yet so vital. Thank you ver much!

Bernhard Barker · Accepted Answer · 2013-02-07 23:15:06Z

2

substring is a pointer, as long as it's pointing to somewhere memory, it will never be null (false).

Replace while(substring) with while(*substring) to look for the \0 character instead.

answered Feb 7, 2013 at 23:15

Bernhard Barker

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Comments

user937635 · Accepted Answer · 2013-02-07 23:38:28Z

0

What's the point of "string" in the search function? You're using the substring variable, but not the string variable.

answered Feb 7, 2013 at 23:38

user937635

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