linux man page for getgrent_r

GETGRENT_R(3)						     Linux Programmer's Manual						     GETGRENT_R(3)

NAME
       getgrent_r, fgetgrent_r - get group file entry reentrantly

SYNOPSIS
       #include <grp.h>

       int getgrent_r(struct group *gbuf, char *buf,
		      size_t buflen, struct group **gbufp);

       int fgetgrent_r(FILE *fp, struct group *gbuf, char *buf,
		       size_t buflen, struct group **gbufp);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getgrent_r(): _GNU_SOURCE
       fgetgrent_r(): _SVID_SOURCE

DESCRIPTION
       The  functions  getgrent_r() and fgetgrent_r() are the reentrant versions of getgrent(3) and fgetgrent(3).  The former reads the next group
       entry from the stream initialized by setgrent(3).  The latter reads the next group entry from the stream fp.

       The group structure is defined in <grp.h> as follows:

	   struct group {
	       char    *gr_name;     /* group name */
	       char    *gr_passwd;   /* group password */
	       gid_t	gr_gid;      /* group ID */
	       char   **gr_mem;      /* group members */
	   };

       The nonreentrant functions return a pointer to static storage, where this static storage contains further pointers to group name,  password
       and  members.  The reentrant functions described here return all of that in caller-provided buffers.  First of all there is the buffer gbuf
       that can hold a struct group.  And next the buffer buf of size buflen that can hold additional strings.	The result of these functions, the
       struct group read from the stream, is stored in the provided buffer *gbuf, and a pointer to this struct group is returned in *gbufp.

RETURN VALUE
       On  success,  these  functions  return  0 and *gbufp is a pointer to the struct group.  On error, these functions return an error value and
       *gbufp is NULL.

ERRORS
       ENOENT No more entries.

       ERANGE Insufficient buffer space supplied.  Try again with larger buffer.

CONFORMING TO
       These functions are GNU extensions, done in a style resembling the POSIX version of functions like getpwnam_r(3).  Other systems use proto-
       type

	   struct group *getgrent_r(struct group *grp, char *buf,
				    int buflen);

       or, better,

	   int getgrent_r(struct group *grp, char *buf, int buflen,
			  FILE **gr_fp);

NOTES
       The function getgrent_r() is not really reentrant since it shares the reading position in the stream with all other threads.

EXAMPLE
       #define _GNU_SOURCE
       #include <grp.h>
       #include <stdio.h>
       #include <stdlib.h>
       #define BUFLEN 4096

       int
       main(void)
       {
	   struct group grp, *grpp;
	   char buf[BUFLEN];
	   int i;

	   setgrent();
	   while (1) {
	       i = getgrent_r(&grp, buf, BUFLEN, &grpp);
	       if (i)
		   break;
	       printf("%s (%d):", grpp->gr_name, grpp->gr_gid);
	       for (i = 0; ; i++) {
		   if (grpp->gr_mem[i] == NULL)
		       break;
		   printf(" %s", grpp->gr_mem[i]);
	       }
	       printf("
");
	   }
	   endgrent();
	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       fgetgrent(3), getgrent(3), getgrgid(3), getgrnam(3), putgrent(3), group(5)

COLOPHON
       This  page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2007-07-26							     GETGRENT_R(3)