getgrent_r(3)
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 buf
- fer.
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 3.25 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/.