GETGRGID(P) GETGRGID(P)
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 reen-
trant 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 con-
tain 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 buf-
size 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 loca-
tion 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() func-
tion 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
POSIX 2003 GETGRGID(P)
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