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GETGRGID(3P)               POSIX Programmer's Manual              GETGRGID(3P)
PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       getgrgid, getgrgid_r -- get group database entry for a group ID
SYNOPSIS
       #include <grp.h>
       struct group *getgrgid(gid_t gid);
       int getgrgid_r(gid_t gid, struct group *grp, char *buffer,
           size_t bufsize, struct group **result);
DESCRIPTION
       The getgrgid() function shall search the group database  for  an  entry
       with a matching gid.
       The getgrgid() function need not be thread-safe.
       The  getgrgid_r()  function shall update the group structure pointed to
       by grp and store a pointer to that structure at the location pointed to
       by  result.   The structure shall contain an entry from the group data-
       base with a matching gid.  Storage referenced by the group structure is
       allocated  from the memory provided with the buffer parameter, which is
       bufsize bytes in size. A call to sysconf(_SC_GETGR_R_SIZE_MAX)  returns
       either  -1 without changing errno or an initial value suggested for the
       size of this buffer.  A null pointer shall be returned at the  location
       pointed to by result on error or if the requested entry is not found.
RETURN VALUE
       Upon  successful  completion,  getgrgid()  shall  return a pointer to a
       struct group with the structure defined  in  <grp.h>  with  a  matching
       entry  if  one  is  found.  The getgrgid() function shall return a null
       pointer if either the requested  entry  was  not  found,  or  an  error
       occurred. On error, errno shall be set to indicate the error.
       The  application  shall  not  modify  the structure to which the return
       value points, nor any storage areas pointed to by pointers  within  the
       structure.  The  returned  pointer,  and pointers within the structure,
       might be invalidated or the structure or the  storage  areas  might  be
       overwritten  by  a subsequent call to getgrent(), getgrgid(), or getgr-
       nam().
       If successful, the getgrgid_r() function shall return zero;  otherwise,
       an error number shall be returned to indicate the error.
ERRORS
       The getgrgid() and getgrgid_r() functions may fail if:
       EIO    An I/O error has occurred.
       EINTR  A signal was caught during getgrgid().
       EMFILE All  file  descriptors  available  to  the process are currently
              open.
       ENFILE The maximum allowable number of files is currently open  in  the
              system.
       The getgrgid_r() function may fail if:
       ERANGE Insufficient storage was supplied via buffer and bufsize to con-
              tain the data to be referenced by the resulting group structure.
       The following sections are informative.
EXAMPLES
       Note that sysconf(_SC_GETGR_R_SIZE_MAX) may return -1 if  there  is  no
       hard  limit  on  the  size of the buffer needed to store all the groups
       returned. This example shows how an application can allocate  a  buffer
       of sufficient size to work with getgrid_r().
           long int initlen = sysconf(_SC_GETGR_R_SIZE_MAX);
           size_t len;
           if (initlen == -1)
               /* Default initial length. */
               len = 1024;
           else
               len = (size_t) initlen;
           struct group result;
           struct group *resultp;
           char *buffer = malloc(len);
           if (buffer == NULL)
               ...handle error...
           int e;
           while ((e = getgrgid_r(42, &result, buffer, len, &resultp)) == ERANGE)
               {
               size_t newlen = 2 * len;
               if (newlen < len)
                   ...handle error...
               len = newlen;
               char *newbuffer = realloc(buffer, len);
               if (newbuffer == NULL)
                   ...handle error...
               buffer = newbuffer;
               }
           if (e != 0)
               ...handle error...
           free (buffer);
   Finding an Entry in the Group Database
       The  following example uses getgrgid() to search the group database for
       a group ID that was previously stored in a stat structure, then  prints
       out  the group name if it is found. If the group is not found, the pro-
       gram prints the numeric value of the group for the entry.
           #include <sys/types.h>
           #include <grp.h>
           #include <stdio.h>
           ...
           struct stat statbuf;
           struct group *grp;
           ...
           if ((grp = getgrgid(statbuf.st_gid)) != NULL)
               printf(" %-8.8s", grp->gr_name);
           else
               printf(" %-8d", statbuf.st_gid);
           ...
APPLICATION USAGE
       Applications wishing to check for error situations should set errno  to
       0  before  calling  getgrgid().   If  errno  is set on return, an error
       occurred.
       The getgrgid_r() function is thread-safe and shall return values  in  a
       user-supplied  buffer instead of possibly using a static data area that
       may be overwritten by each call.
       Portable applications should take into account that it is usual for  an
       implementation  to return -1 from sysconf() indicating that there is no
       maximum for _SC_GETGR_R_SIZE_MAX.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       endgrent(), getgrnam(), sysconf()
       The Base Definitions volume of POSIX.1-2008, <grp.h>, <sys_types.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained  online
       at http://www.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                         GETGRGID(3P)