putenv.c

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· C语言 代码 · 共 136 行

#ifndef lint
static char *sccsid = "@(#)putenv.c	4.1      (ULTRIX)        7/2/90";
#endif lint

/************************************************************************
 *									*
 *			Copyright (c) 1986 by				*
 *		Digital Equipment Corporation, Maynard, MA		*
 *			All rights reserved.				*
 *									*
 *   This software is furnished under a license and may be used and	*
 *   copied  only  in accordance with the terms of such license and	*
 *   with the  inclusion  of  the  above  copyright  notice.   This	*
 *   software  or  any  other copies thereof may not be provided or	*
 *   otherwise made available to any other person.  No title to and	*
 *   ownership of the software is hereby transferred.			*
 *									*
 *   This software is  derived  from  software  received  from  the	*
 *   University    of   California,   Berkeley,   and   from   Bell	*
 *   Laboratories.  Use, duplication, or disclosure is  subject  to	*
 *   restrictions  under  license  agreements  with  University  of	*
 *   California and with AT&T.						*
 *									*
 *   The information in this software is subject to change  without	*
 *   notice  and should not be construed as a commitment by Digital	*
 *   Equipment Corporation.						*
 *									*
 *   Digital assumes no responsibility for the use  or  reliability	*
 *   of its software on equipment which is not supplied by Digital.	*
 *									*
 ************************************************************************/

/*
 *	Portions of this software have been licensed to 
 *	Digital Equipment Company, Maynard, MA.
 *	Copyright (c) 1987 Sun Microsystems, Inc.  ALL RIGHTS RESERVED.
 */
/*
 *	Modification History:
 * 
 *      10 Nov 89 -- lebel
 *		Added copyright header.
 *
 */

/*	LINTLIBRARY	*/
/*	putenv - change environment variables

	input - char *change = a pointer to a string of the form
			       "name=value"

	output - 0, if successful
		 1, otherwise
*/
#define NULL 0
extern char **environ;		/* pointer to enviroment */
static reall;		/* flag to reallocate space, if putenv is called
				   more than once */

int
putenv(change)
char *change;
{
	char **newenv;		    /* points to new environment */
	register int which;	    /* index of variable to replace */
	char *realloc(), *malloc(); /* memory alloc routines */

	if ((which = find(change)) < 0)  {
		/* if a new variable */
		/* which is negative of table size, so invert and
		   count new element */
		which = (-which) + 1;
		if (reall)  {
			/* we have expanded environ before */
			newenv = (char **)realloc(environ,
				  which*sizeof(char *));
			if (newenv == NULL)  return -1;
			/* now that we have space, change environ */
			environ = newenv;
		} else {
			/* environ points to the original space */
			reall++;
			newenv = (char **)malloc(which*sizeof(char *));
			if (newenv == NULL)  return -1;
			(void)memcpy((char *)newenv, (char *)environ,
 				(int)(which*sizeof(char *)));
			environ = newenv;
		}
		environ[which-2] = change;
		environ[which-1] = NULL;
	}  else  {
		/* we are replacing an old variable */
		environ[which] = change;
	}
	return 0;
}

/*	find - find where s2 is in environ
 *
 *	input - str = string of form name=value
 *
 *	output - index of name in environ that matches "name"
 *		 -size of table, if none exists
*/
static
find(str)
register char *str;
{
	register int ct = 0;	/* index into environ */

	while(environ[ct] != NULL)   {
		if (match(environ[ct], str)  != 0)
			return ct;
		ct++;
	}
	return -(++ct);
}
/*
 *	s1 is either name, or name=value
 *	s2 is name=value
 *	if names match, return value of 1,
 *	else return 0
 */

static
match(s1, s2)
register char *s1, *s2;
{
	while(*s1 == *s2++)  {
		if (*s1 == '=')
			return 1;
		s1++;
	}
	return 0;
}