getenv.c

来自「操作系统SunOS 4.1.3版本的源码」· C语言 代码 · 共 46 行

#if !defined(lint) && defined(SCCSIDS)
static	char sccsid[] = "@(#)getenv.c 1.1 92/07/30 SMI"; /* from S5R2 1.2 */
#endif

/*LINTLIBRARY*/
/*
 *	getenv(name)
 *	returns ptr to value associated with name, if any, else NULL
 */
#define NULL	0
extern char **environ;
static char *nvmatch();

char *
getenv(name)
register char *name;
{
	register char *v, **p=environ;

	if(p == NULL)
		return(NULL);
	while(*p != NULL)
		if((v = nvmatch(name, *p++)) != NULL)
			return(v);
	return(NULL);
}

/*
 *	s1 is either name, or name=value
 *	s2 is name=value
 *	if names match, return value of s2, else NULL
 *	used for environment searching: see getenv
 */

static char *
nvmatch(s1, s2)
register char *s1, *s2;
{
	while(*s1 == *s2++)
		if(*s1++ == '=')
			return(s2);
	if(*s1 == '\0' && *(s2-1) == '=')
		return(s2);
	return(NULL);
}