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Linux 2.6 - man page for fgetgrent_r (linux section 3)

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  set-
       grent(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 */
	   };

       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 buffer.

CONFORMING TO
       These functions are GNU extensions, done in a style resembling the POSIX version of  func-
       tions like getpwnam_r(3).  Other systems use 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 3.55 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					    2010-10-21				    GETGRENT_R(3)


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