strtok.c

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/*
 * Get next token from string s (NULL on 2nd, 3rd, etc. calls),
 * where tokens are nonempty strings separated by runs of
 * chars from delim.  Writes NULs into s to end tokens.  delim need not
 * remain constant from call to call.
 *
 * Copyright (c) Henry Spencer.
 * Written by Henry Spencer.
 *
 * This software is not subject to any license of the American Telephone
 * and Telegraph Company or of the Regents of the University of California.
 *
 * Permission is granted to anyone to use this software for any purpose on
 * any computer system, and to alter it and 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 flaws in it.
 *
 * 2. The origin of this software must not be misrepresented, either by
 *    explicit claim or by omission.  Since few users ever read sources,
 *    credits must appear in the documentation.
 *
 * 3. Altered versions must be plainly marked as such, and must not be
 *    misrepresented as being the original software.  Since few users
 *    ever read sources, credits must appear in the documentation.
 *
 * 4. This notice may not be removed or altered.
 */

#define	NULL	0
#define CONST

static char *scanpoint = NULL;

char *				/* NULL if no token left */
     strtok(s, delim)
     char *s;
     register CONST char *delim;
{
	register char *scan;
	char *tok;
	register CONST char *dscan;

	if (s == NULL && scanpoint == NULL)
		return (NULL);
	if (s != NULL)
		scan = s;
	else
		scan = scanpoint;

	/*
	 * Scan leading delimiters.
	 */
	for (; *scan != '\0'; scan++) {
		for (dscan = delim; *dscan != '\0'; dscan++)
			if (*scan == *dscan)
				break;
		if (*dscan == '\0')
			break;
	}
	if (*scan == '\0') {
		scanpoint = NULL;
		return (NULL);
	}
	tok = scan;

	/*
	 * Scan token.
	 */
	for (; *scan != '\0'; scan++) {
		for (dscan = delim; *dscan != '\0';)	/* ++ moved down. */
			if (*scan == *dscan++) {
				scanpoint = scan + 1;
				*scan = '\0';
				return (tok);
			}
	}

	/*
	 * Reached end of string.
	 */
	scanpoint = NULL;
	return (tok);
}