String replace in pure C

str_replace.c

/*
 * @brief
 * PHP's str_replace ported to C
 * @author Silver Moon (m00n.silv3r@gmail.com)
 * */
 
#include<stdio.h>
#include<string.h>
#include<stdlib.h>

char *str_replace(char *search , char *replace , char *subject);

int main()
{
	char *a = "allblldddlll";
	char *c = str_replace("ll" , "xll" , a);
	puts(c);
	return 0;
}

/*
 * Search and replace a string with another string , in a string
 * */
char *str_replace(char *search , char *replace , char *subject)
{
	char  *p = NULL , *old = NULL , *new_subject = NULL ;
	int c = 0 , search_size;
	
	search_size = strlen(search);
	
	//Count how many occurences
	for(p = strstr(subject , search) ; p != NULL ; p = strstr(p + search_size , search))
	{
		c++;
	}
	
	//Final size
	c = ( strlen(replace) - search_size )*c + strlen(subject);
	
	//New subject with new size
	new_subject = malloc( c );
	
	//Set it to blank
	strcpy(new_subject , "");
	
	//The start position
	old = subject;
	
	for(p = strstr(subject , search) ; p != NULL ; p = strstr(p + search_size , search))
	{
		//move ahead and copy some text from original subject , from a certain position
		strncpy(new_subject + strlen(new_subject) , old , p - old);
		
		//move ahead and copy the replacement text
		strcpy(new_subject + strlen(new_subject) , replace);
		
		//The new start position after this search match
		old = p + search_size;
	}
	
	//Copy the part after the last search match
	strcpy(new_subject + strlen(new_subject) , old);
	
	return new_subject;
}