replace.c

/********************
 * Exemplo de replace em C.
 * Por Luiz Felipe.
 *     https://github.com/Silva97
 ********************/

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

int replace(char *text, char *word, char *new);
	
int main(){
	char text[20] = "Apenas um teste.";
	replace(text, "um", "dois");
	puts(text);
	return 0;
}

int replace(char *text, char *word, char *new){
	char *start;
	int   sizew = strlen(word),
	      sizen = strlen(new);
	
	start = strstr(text, word);
	if(!start)
		return 0;
	
	strcpy(start + sizen, start + sizew);
	memmove(start, new, sizen);
	
	return 1;
}