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 *stream, 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():
	   Since glibc 2.19:
	       _DEFAULT_SOURCE
	   Glibc 2.19 and earlier:
	       _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 stream.

       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;	       /* NULL-terminated array of pointers
					  to names of group members */
	   };

       For more information about the fields of this structure, see group(5).

       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 buf-
	      fer.

ATTRIBUTES
       For  an	explanation  of	 the  terms  used   in	 this	section,   see
       attributes(7).

       +--------------+---------------+-----------------------------+
       |Interface     | Attribute     | Value			    |
       +--------------+---------------+-----------------------------+
       |getgrent_r()  | Thread safety | MT-Unsafe race:grent locale |
       +--------------+---------------+-----------------------------+
       |fgetgrent_r() | Thread safety | MT-Safe			    |
       +--------------+---------------+-----------------------------+
       In  the	above  table, grent in race:grent signifies that if any of the
       functions setgrent(), getgrent(), endgrent(), or getgrent_r() are  used
       in  parallel  in	 different threads of a program, then data races could
       occur.

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

	   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("\n");
	   }
	   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 4.10 of the Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       https://www.kernel.org/doc/man-pages/.



GNU				  2016-03-15			 GETGRENT_R(3)