GETGRGID(3) Library Functions Manual GETGRGID(3)

getgrgid getgrgid_r — get group database entry for a group ID

#include <grp.h>

struct group *getgrgid(gid_t gid);
[TSF] int getgrgid_r(gid_t gid, struct group *grp, char *buffer,
       size_t bufsize, struct group **result);

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.

[TSF] The getgrgid_r () function shall update the structure pointed to by 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 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(3) parameter. A NULL pointer shall be returned at the location pointed to by result on error or if the requested entry is not found.

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(3), getgrgid (), or getgrnam(3).

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

The getgrgid () and getgrgid_r () functions may fail if:

An I/O error has occurred.
A signal was caught during getgrgid ().
{OPEN_MAX} file descriptors are currently open in the calling process.
The maximum allowable number of files is currently open in the system.

[TSF] The getgrgid_r () function may fail if:

[TSF] Insufficient storage was supplied via buffer and bufsize to contain the data to be referenced by the resulting group structure.

The following example uses getgrgid () to search the group database for a group ID that was previously stored in a 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);
...

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.

None.

None.

endgrent(3), getgrnam(3), the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <grp.h>, <limits.h>, <sys/types.h>

First released in Issue 1. Derived from System V Release 2.0.

Normative text previously in the APPLICATION USAGE section is moved to the RETURN VALUE section.

The getgrgid_r () function is included for alignment with the POSIX Threads Extension.

A note indicating that the getgrgid () function need not be reentrant is added to the DESCRIPTION.

The getgrgid_r () function is marked as part of the Thread-Safe Functions option.

The Open Group Corrigendum U028/3 is applied, correcting text in the DESCRIPTION describing matching the gid.

In the DESCRIPTION, the note about reentrancy is expanded to cover thread-safety.

In the SYNOPSIS, the optional include of the <sys/types.h> header is removed.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

  • The requirement to include <sys/types.h> has been removed. Although <sys/types.h> was required for conforming implementations of previous POSIX specifications, it was not required for UNIX applications.
  • In the RETURN VALUE section, the requirement to set errno on error is added.
  • The [EIO], [EINTR], [EMFILE], and [ENFILE] optional error conditions are added.

The APPLICATION USAGE section is updated to include a note on the thread-safe function and its avoidance of possibly using a static data area.

IEEE PASC Interpretation 1003.1 #116 is applied, changing the description of the size of the buffer from bufsize characters to bytes.

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January 1, 2004 posix.fail