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GETGRENT_R
Section: Linux Programmer's Manual (3)
Updated: 2007-07-26
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NAME
getgrent_r, fgetgrent_r - get group file entry reentrantly
SYNOPSIS
#include <grp.h>
int getgrent_r(struct group *gbuf, char *buf,
size_t buflen, struct group **gbufp);
int fgetgrent_r(FILE *fp, struct group *gbuf, char *buf,
size_t buflen, struct group **gbufp);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
getgrent_r():
_GNU_SOURCE
fgetgrent_r():
_SVID_SOURCE
DESCRIPTION
The functions
getgrent_r()
and
fgetgrent_r()
are the reentrant versions of
getgrent(3)
and
fgetgrent(3).
The former reads the next group entry from the stream initialized by
setgrent(3).
The latter reads the next group entry from the stream
fp.
The group structure is defined in
<grp.h>
as follows:
struct group {
char *gr_name; /* group name */
char *gr_passwd; /* group password */
gid_t gr_gid; /* group ID */
char **gr_mem; /* group members */
};
The nonreentrant functions return a pointer to static storage,
where this static storage contains further pointers to group
name, password and members.
The reentrant functions described here return all of that in
caller-provided buffers.
First of all there is the buffer
gbuf
that can hold a struct group.
And next the buffer
buf
of size
buflen
that can hold additional strings.
The result of these functions, the struct group read from the stream,
is stored in the provided buffer
*gbuf,
and a pointer to this struct group is returned in
*gbufp.
RETURN VALUE
On success, these functions return 0 and
*gbufp
is a pointer to the struct group.
On error, these functions return an error value and
*gbufp
is NULL.
ERRORS
- ENOENT
-
No more entries.
- ERANGE
-
Insufficient buffer space supplied.
Try again with larger buffer.
CONFORMING TO
These functions are GNU extensions, done in a style resembling
the POSIX version of functions like
getpwnam_r(3).
Other systems use prototype
struct group *getgrent_r(struct group *grp, char *buf,
int buflen);
or, better,
int getgrent_r(struct group *grp, char *buf, int buflen,
FILE **gr_fp);
NOTES
The function
getgrent_r()
is not really reentrant since it shares the reading position
in the stream with all other threads.
EXAMPLE
#define _GNU_SOURCE
#include <grp.h>
#include <stdio.h>
#include <stdlib.h>
#define BUFLEN 4096
int
main(void)
{
struct group grp, *grpp;
char buf[BUFLEN];
int i;
setgrent();
while (1) {
i = getgrent_r(&grp, buf, BUFLEN, &grpp);
if (i)
break;
printf("%s (%d):", grpp->gr_name, grpp->gr_gid);
for (i = 0; ; i++) {
if (grpp->gr_mem[i] == NULL)
break;
printf(" %s", grpp->gr_mem[i]);
}
printf("\n");
}
endgrent();
exit(EXIT_SUCCESS);
}
SEE ALSO
fgetgrent(3),
getgrent(3),
getgrgid(3),
getgrnam(3),
putgrent(3),
group(5)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- EXAMPLE
-
- SEE ALSO
-
- COLOPHON
-
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