getgrent_r, fgetgrent_r — get group file entry reentrantly
#define _GNU_SOURCE #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); |
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 given as parameter.
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 non-reentrant 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.
No more entries.
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>
#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), feature_test_macros(7)
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