getgrgid_r

       #include <sys/types.h>
       #include <grp.h>

       struct group *getgrnam(const char *name);

       struct group *getgrgid(gid_t gid);

       int getgrnam_r(const char *name, struct group *grp,
                 char *buf, size_t buflen, struct group **result);

       int getgrgid_r(gid_t gid, struct group *grp,
                 char *buf, size_t buflen, struct group **result);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getgrnam_r(), getgrgid_r():
           _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _BSD_SOURCE ||
           _SVID_SOURCE || _POSIX_SOURCE

DESCRIPTION
       The getgrnam() function returns a pointer to a structure containing the
       broken-out  fields of the record in the group database (e.g., the local
       group file /etc/group, NIS, and LDAP) that matches the group name name.

       The getgrgid() function returns a pointer to a structure containing the
       broken-out  fields of the record in the group database that matches the
       group ID gid.

       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 getgrnam_r() and getgrgid_r() functions obtain the same information
       as  getgrnam()  and getgrgid(), but store the retrieved group structure
       in the space pointed to by grp.  The string fields pointed  to  by  the
       members  of  the  group  structure are stored in the buffer buf of size
       buflen.  A pointer to the result (in case of success) or NULL (in  case
       no entry was found or an error occurred) is stored in *result.

       The call

           sysconf(_SC_GETGR_R_SIZE_MAX)

       returns either -1, without changing errno, or an initial suggested size
       for buf.  (If this size is too small, the call fails  with  ERANGE,  in
       which case the caller can retry with a larger buffer.)
       On  success, getgrnam_r() and getgrgid_r() return zero, and set *result
       to grp.  If no matching group record was found, these functions  return
       0  and  store  NULL  in  *result.  In case of error, an error number is
       returned, and NULL is stored in *result.

ERRORS
       0 or ENOENT or ESRCH or EBADF or EPERM or ...
              The given name or gid was not found.

       EINTR  A signal was caught.

       EIO    I/O error.

       EMFILE The per-process limit on the number of open file descriptors has
              been reached.

       ENFILE The system-wide limit on the total number of open files has been
              reached.

       ENOMEM Insufficient memory to allocate group structure.

       ERANGE Insufficient buffer space supplied.

FILES
       /etc/group
              local group database file

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

       +--------------+---------------+-----------------------------+
       |Interface     | Attribute     | Value                       |
       +--------------+---------------+-----------------------------+
       |getgrnam()    | Thread safety | MT-Unsafe race:grnam locale |
       +--------------+---------------+-----------------------------+
       |getgrgid()    | Thread safety | MT-Unsafe race:grgid locale |
       +--------------+---------------+-----------------------------+
       |getgrnam_r(), | Thread safety | MT-Safe locale              |
       |getgrgid_r()  |               |                             |
       +--------------+---------------+-----------------------------+
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

NOTES
       The  formulation  given above under "RETURN VALUE" is from POSIX.1.  It
       does not call "not found" an error, hence does not specify  what  value
       errno  might  have  in this situation.  But that makes it impossible to
       recognize errors.  One might argue that according to POSIX errno should
       be  left  unchanged  if  an entry is not found.  Experiments on various
       UNIX-like systems show that lots of different values occur in this sit-
       uation:  0, ENOENT, EBADF, ESRCH, EWOULDBLOCK, EPERM, and probably oth-
       ers.
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