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 reentrant. A function that is not
required to be reentrant is not required to 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 database
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. The maximum size needed for this buffer can be
determined with the {_SC_GETGR_R_SIZE_MAX} sysconf() parameter. 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 return value may point to a static area which is overwritten by a
subsequent call to getgrent(), getgrgid(), or getgrnam().
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 {OPEN_MAX} file descriptors are currently open in the calling
process.
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
contain the data to be referenced by the resulting group
structure.
The following sections are informative.
EXAMPLES
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
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);
...
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.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
endgrent() , getgrnam() , the Base Definitions volume of
IEEE Std 1003.1-2001, <grp.h>, <limits.h>, <sys/types.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .