|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
|
|
|
getgrent_r(3) Library Functions Manual getgrent_r(3)
getgrent_r, fgetgrent_r - get group file entry reentrantly
Standard C library (libc, -lc)
#include <grp.h>
int getgrent_r(size_t size;
struct group *restrict gbuf,
char buf[restrict size], size_t size,
struct group **restrict gbufp);
int fgetgrent_r(size_t size;
FILE *restrict stream, struct group *restrict gbuf,
char buf[restrict size], size_t size,
struct group **restrict gbufp);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
getgrent_r():
_GNU_SOURCE
fgetgrent_r():
Since glibc 2.19:
_DEFAULT_SOURCE
glibc 2.19 and earlier:
_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 stream.
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; /* NULL-terminated array of pointers
to names of 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 size 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.
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────┬───────────────┬────────────────────────────────┐
│ Interface │ Attribute │ Value │
├───────────────┼───────────────┼────────────────────────────────┤
│ getgrent_r() │ Thread safety │ MT-Unsafe race:grent locale │
├───────────────┼───────────────┼────────────────────────────────┤
│ fgetgrent_r() │ Thread safety │ MT-Safe │
└───────────────┴───────────────┴────────────────────────────────┘
In the above table, grent in race:grent signifies that if any of
the functions setgrent(3), getgrent(3), endgrent(3), or
getgrent_r() are used in parallel in different threads of a
program, then data races could occur.
Other systems use the prototype
struct group *getgrent_r(struct group *grp, char buf[.size],
int size);
or, better,
int getgrent_r(struct group *grp, char buf[.size], int size,
FILE **gr_fp);
GNU.
These functions are done in a style resembling the POSIX version
of functions like getpwnam_r(3).
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 <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#define BUFLEN 4096
int
main(void)
{
struct group grp;
struct group *grpp;
char buf[BUFLEN];
int i;
setgrent();
while (1) {
i = getgrent_r(&grp, buf, sizeof(buf), &grpp);
if (i)
break;
printf("%s (%jd):", grpp->gr_name, (intmax_t) grpp->gr_gid);
for (size_t j = 0; ; j++) {
if (grpp->gr_mem[j] == NULL)
break;
printf(" %s", grpp->gr_mem[j]);
}
printf("\n");
}
endgrent();
exit(EXIT_SUCCESS);
}
fgetgrent(3), getgrent(3), getgrgid(3), getgrnam(3), putgrent(3),
group(5)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-06-28 getgrent_r(3)
Pages that refer to this page: fgetgrent(3), getgrent(3)
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|