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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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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 *stream, 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():
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 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.
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.
These functions are GNU extensions, done in a style resembling
the POSIX version of functions like getpwnam_r(3). Other systems
use the 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 <stdint.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 (int 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 release 5.10 of the Linux man-pages project.
A description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2020-11-01 GETGRENT_R(3)
Pages that refer to this page: fgetgrent(3), getgrent(3)
Copyright and license for this manual page
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