| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON | The Linux Programming Interface |
GETGRENT_R(3) Linux Programmer's Manual GETGRENT_R(3)
getgrent_r, fgetgrent_r - get group file entry reentrantly
#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
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 */
};
For more information about the fields of this structure, see group(5).
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.
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.
ENOENT No more entries.
ERANGE Insufficient buffer space supplied. Try again with larger buffer.
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);
The function getgrent_r() is not really reentrant since it shares the reading
position in the stream with all other threads.
#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);
}
fgetgrent(3), getgrent(3), getgrgid(3), getgrnam(3), putgrent(3), group(5)
This page is part of release 3.32 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/.
GNU 2010-10-21 GETGRENT_R(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface