getgroups

getgroups

Determine Supplementary Group IDs

Portability: POSIX.1 conforming

SYNOPSIS
DESCRIPTION
RETURN VALUE
EXAMPLE
RELATED FUNCTIONS

SYNOPSIS

#include <sys/types.h>
#include <unistd.h>

int getgroups(int listSize, gid_t *groupList);

DESCRIPTION

getgroups stores the supplementary group IDs of the calling process in an array.

listSize

is the number of elements that can be stored in the array.

groupList

is a pointer to the beginning of the array used to store the supplementary user IDs.

Note: Note that groupList is declared as gid_t *groupList so that NULL may be passed to groupList when listSize is 0 . This could not be done if groupList was declared as an array. [cautionend]

RETURN VALUE

getgroups returns the number of supplementary group IDs in groupList . This value is always less than or equal to the value of NGROUPS_MAX defined in <limits.h> . If listSize is 0 , getgroups returns the total number of supplementary group IDs and does not store the group IDs in an array. getgroups returns a -1 if unsuccessful.

EXAMPLE

The following example illustrates the use of getgroups to determine supplementary group IDs.

Note: You must specify the posix option when compiling this example. [cautionend]

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <limits.h>

main()
{
   gid_t groupIDs[NGROUPS_MAX];
   int i, count;

   if ((count = getgroups(NGROUPS_MAX, groupIDs)) == -1)
      perror("getgroups error");
   else
      for (i = 0; i < count; i++)
         printf("Group ID %d = %d\n", i + 1, (int) groupIDs[i]);
}

RELATED FUNCTIONS

getgroupsbyname

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