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 *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
              buffer.

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 5.05 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)