getgrent_r man page on ElementaryOS

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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 */
	   };

       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.

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

	   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 3.54 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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