regsub.c

/*
 * regsub
 *
 *  Copyright (c) 1986 by University of Toronto.
 *  Written by Henry Spencer.  Not derived from licensed software.
 *
 *  Permission is granted to anyone to use this software for any
 *  purpose on any computer system, and to redistribute it freely,
 *  subject to the following restrictions:
 *
 *  1. The author is not responsible for the consequences of use of
 *      this software, no matter how awful, even if they arise
 *      from defects in it.
 *
 *  2. The origin of this software must not be misrepresented, either
 *      by explicit claim or by omission.
 *
 *  3. Altered versions must be plainly marked as such, and must not
 *      be misrepresented as being the original software.
 */
#include <stdio.h>
#include <string.h>
#include "regexp.h"
#include "regmagic.h"

#ifndef CHARBITS
#define UCHARAT(p)  ((int)*(unsigned char *)(p))
#else
#define UCHARAT(p)  ((int)*(p)&CHARBITS)
#endif

/*
 - regsub - perform substitutions after a regexp match
 */
void
hs_regsub(prog, source, dest)
const hs_regexp *prog;
const char *source;
char *dest;
{
    register char *src;
    register char *dst;
    register char c;
    register int no;
    register int len;

    if (prog == NULL || source == NULL || dest == NULL) {
        hs_regerror("NULL parm to regsub");
        return;
    }
    if (UCHARAT(prog->program) != MAGIC) {
        hs_regerror("damaged regexp fed to regsub");
        return;
    }

    src = (char *)source;
    dst = dest;
    while ((c = *src++) != '\0') {
        if (c == '&')
            no = 0;
        else if (c == '\\' && '0' <= *src && *src <= '9')
            no = *src++ - '0';
        else
            no = -1;
        if (no < 0) {   /* Ordinary character. */
            if (c == '\\' && (*src == '\\' || *src == '&'))
                c = *src++;
            *dst++ = c;
        } else if (prog->startp[no] != NULL && prog->endp[no] != NULL) {
            len = prog->endp[no] - prog->startp[no];
            (void) strncpy(dst, prog->startp[no], len);
            dst += len;
            if (len != 0 && *(dst-1) == '\0') { /* strncpy hit NUL. */
                hs_regerror("damaged match string");
                return;
            }
        }
    }
    *dst++ = '\0';
}