strrepl.c

Many C samples. It is a good sample for students to learn C language.

/*  File   : strrepl.c
    Author : Richard A. O'Keefe.
    Updated: 23 April 1984
    Defines: strrepl()

    strrepl(dst, src, pat, rep, times) copies src to dst, replacing  the
    first "times" non-overlapping instances of pat by rep.  pat is not a
    regex(3) pattern, it is a  literal  string  which  must  be  matched
    exactly.   As  a  special hack, since strfind claims to find "" just
    once at the end of the src string, strrepl does a strcat when pat is
    an empty string "".  If times <= 0, it is just strmov.

    The result is a pointer to the NUL which now terminates dst.

    BEWARE: even when rep is shorter than pat it is NOT necessarily safe
    for dst to be the same as src.  ALWAYS make sure dst and src do not/
    will not overlap.  You have been warned.

    There really ought to be a strnrepl with a bound for the size of the
    destination string, but there isn't.
*/

#include "strings.h"
#include "_str2pat.h"

char *strrepl(dst, src, pat, rep, times)
    char *dst, *src, *pat, *rep;
    int times;
    {
	register char *s, *p;
	register int c, lastch;

	pat = _str2pat(pat);
	if (times <= 0) {
	    for (p = dst, s = src; *p++ = *s++; ) ;
	    return p-1;
	}
	if (_pat_lim < 0) {
	    for (p = dst, s = src; *p++ = *s++; ) ;
	    for (--p, s = rep; *p++ = *s++; ) ;
	    return p-1;
 	}
	/*  The pattern is non-empty and times is positive  */
	c = _pat_lim, lastch = pat[c];
	for (;;) {
	    for (s = src, p = dst; --c >= 0; )
		if (!(*p++ = *s++)) return p-1;
	    c = *s, src = s, dst = p;
	    if (c == lastch) {
		for (s -= _pat_lim, p = pat; *p; )
		    if (*s++ != *p++) goto not_yet;
		for (p = dst-_pat_lim, s = rep; *p++ = *s++; ) ;
		--p;
		if (--times == 0) {
		    for (s = src; *p++ = *++s; ) ;
		    return p-1;
		}
		dst = p, src++, c = _pat_lim;
	    } else {
not_yet:	c = _pat_vec[c];
	    }
	}
    }