GETGRGID(3)                POSIX Programmer's Manual               GETGRGID(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       getgrgid, getgrgid_r -- get group database entry for a group ID

SSYYNNOOPPSSIISS
       #include <grp.h>

       struct group *getgrgid(gid_t _g_i_d);
       int getgrgid_r(gid_t _g_i_d, struct group *_g_r_p, char *_b_u_f_f_e_r,
           size_t _b_u_f_s_i_z_e, struct group **_r_e_s_u_l_t);

DDEESSCCRRIIPPTTIIOONN
       The _g_e_t_g_r_g_i_d() function shall search the group database for an entry
       with a matching _g_i_d.

       The _g_e_t_g_r_g_i_d() function need not be thread-safe.

       Applications wishing to check for error situations should set _e_r_r_n_o to
       0 before calling _g_e_t_g_r_g_i_d().  If _g_e_t_g_r_g_i_d() returns a null pointer and
       _e_r_r_n_o is set to non-zero, an error occurred.

       The _g_e_t_g_r_g_i_d___r() function shall update the ggrroouupp structure pointed to
       by _g_r_p and store a pointer to that structure at the location pointed to
       by _r_e_s_u_l_t.  The structure shall contain an entry from the group
       database with a matching _g_i_d.  Storage referenced by the group
       structure is allocated from the memory provided with the _b_u_f_f_e_r
       parameter, which is _b_u_f_s_i_z_e bytes in size. A call to
       _s_y_s_c_o_n_f(_SC_GETGR_R_SIZE_MAX) returns either -1 without changing _e_r_r_n_o
       or an initial value suggested for the size of this buffer.  A null
       pointer shall be returned at the location pointed to by _r_e_s_u_l_t on error
       or if the requested entry is not found.

RREETTUURRNN VVAALLUUEE
       Upon successful completion, _g_e_t_g_r_g_i_d() shall return a pointer to a
       ssttrruucctt ggrroouupp with the structure defined in _<_g_r_p_._h_> with a matching
       entry if one is found. The _g_e_t_g_r_g_i_d() function shall return a null
       pointer if either the requested entry was not found, or an error
       occurred. If the requested entry was not found, _e_r_r_n_o shall not be
       changed. On error, _e_r_r_n_o 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 _g_e_t_g_r_e_n_t(), _g_e_t_g_r_g_i_d(), or
       _g_e_t_g_r_n_a_m().  The returned pointer, and pointers within the structure,
       might also be invalidated if the calling thread is terminated.

       If successful, the _g_e_t_g_r_g_i_d___r() function shall return zero; otherwise,
       an error number shall be returned to indicate the error.

EERRRROORRSS
       The _g_e_t_g_r_g_i_d() and _g_e_t_g_r_g_i_d___r() functions may fail if:

       EEIIOO    An I/O error has occurred.

       EEIINNTTRR  A signal was caught during _g_e_t_g_r_g_i_d().

       EEMMFFIILLEE All file descriptors available to the process are currently
              open.

       EENNFFIILLEE The maximum allowable number of files is currently open in the
              system.

       The _g_e_t_g_r_g_i_d___r() function may fail if:

       EERRAANNGGEE Insufficient storage was supplied via _b_u_f_f_e_r and _b_u_f_s_i_z_e to
              contain the data to be referenced by the resulting ggrroouupp
              structure.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
       Note that _s_y_s_c_o_n_f(_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 _g_e_t_g_r_i_d___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);

   FFiinnddiinngg aann EEnnttrryy iinn tthhee GGrroouupp DDaattaabbaassee
       The following example uses _g_e_t_g_r_g_i_d() to search the group database for
       a group ID that was previously stored in a ssttaatt structure, then prints
       out the group name if it is found. If the group is not found, the
       program 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);
           ...

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       The _g_e_t_g_r_g_i_d___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 _s_y_s_c_o_n_f() indicating that there is no
       maximum for _SC_GETGR_R_SIZE_MAX.

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _e_n_d_g_r_e_n_t(), _g_e_t_g_r_n_a_m(), _s_y_s_c_o_n_f()

       The Base Definitions volume of POSIX.1-2017, <<ggrrpp..hh>>, <<ssyyss__ttyyppeess..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  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.opengroup.org/unix/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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                          GETGRGID(3)
