Originální popis anglicky:
getgroups - get supplementary group IDs
Návod, kniha: POSIX Programmer's Manual
#include <unistd.h>
int getgroups(int
gidsetsize, gid_t
grouplist []);
The
getgroups() function shall fill in the array
grouplist with
the current supplementary group IDs of the calling process. It is
implementation-defined whether
getgroups() also returns the effective
group ID in the
grouplist array.
The
gidsetsize argument specifies the number of elements in the array
grouplist. The actual number of group IDs stored in the array shall be
returned. The values of array entries with indices greater than or equal to
the value returned are undefined.
If
gidsetsize is 0,
getgroups() shall return the number of group
IDs that it would otherwise return without modifying the array pointed to by
grouplist.
If the effective group ID of the process is returned with the supplementary
group IDs, the value returned shall always be greater than or equal to one and
less than or equal to the value of {NGROUPS_MAX}+1.
Upon successful completion, the number of supplementary group IDs shall be
returned. A return value of -1 indicates failure and
errno shall be set
to indicate the error.
The
getgroups() function shall fail if:
- EINVAL
- The gidsetsize argument is non-zero and less than
the number of group IDs that would have been returned.
The following sections are informative.
The following example places the current supplementary group IDs of the calling
process into the
group array.
#include <sys/types.h>
#include <unistd.h>
...
gid_t *group;
int nogroups;
long ngroups_max;
ngroups_max = sysconf(_SC_NGROUPS_MAX) + 1;
group = (gid_t *)malloc(ngroups_max *sizeof(gid_t));
ngroups = getgroups(ngroups_max, group);
None.
The related function
setgroups() is a privileged operation and therefore
is not covered by this volume of IEEE Std 1003.1-2001.
As implied by the definition of supplementary groups, the effective group ID may
appear in the array returned by
getgroups() or it may be returned only
by
getegid(). Duplication may exist, but the application needs to call
getegid() to be sure of getting all of the information. Various
implementation variations and administrative sequences cause the set of groups
appearing in the result of
getgroups() to vary in order and as to
whether the effective group ID is included, even when the set of groups is the
same (in the mathematical sense of "set"). (The history of a process
and its parents could affect the details of the result.)
Application writers should note that {NGROUPS_MAX} is not necessarily a constant
on all implementations.
None.
getegid() ,
setgid() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<sys/types.h>,
<unistd.h>
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
.
