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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 *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 4.15 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                               2017-09-15                     GETGRENT_R(3)