Using PCRE in C to do string replacement

[bluedalmatian]

I'm experimenting with PCRE. I can do simple matching to determine if a match was found or not but I can't get replacement to work and I cant find an example on the web of how to do it.

Am I right in thinking that PCRE can replace the matched part of the input with a new string by writing into an array the start & finish index of the match?

The following little program is supposed to replace the 61 with 63 but the result value keeps coming out as 2 (error). I suspect Im doing something wrong with that ovector array?

Thanks

#include <stdio.h>
#include <pcre.h>
#include <string.h>
int main()
{
//look at the str 612780 and see if it starts with 61

pcre *regexp;
const char *error;
int erroffset;
char *pattern = "^61([0-9]+)$";
char *string = "612000";
char* replacement = "63";
regexp = pcre_compile(pattern,0,&error,&erroffset,NULL);
if (!regexp)
{
printf("Error compiling expression\n");
exit(1);

}
int result;

int ovectorlength = 30;
int ovector[ovectorlength];
result = pcre_exec(regexp,NULL,string,strlen(string),0,0,ov ector,ovectorlength);


//result = 0 means found, -1 not found, other value error
printf("Result: %d\n",result);

if (result == 0)
{

//match found, locate it and do replacement

//??=which elements should i put in here

int start = ovector[???]; //start of match
int end = (ovector[????]);//end of match
//...do replacement here
}

pcre_free(regexp);

return (0);
}