Originální popis anglicky:
getgrent_r, fgetgrent_r - get group file entry reentrantly
Návod, kniha: Linux Programmer's Manual
#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.
- ENOENT
- No more entries.
- ERANGE
- Insufficient buffer space supplied. Try again with larger
buffer.
#define _GNU_SOURCE
#include <grp.h>
#include <stdio.h>
#define BUFLEN 4096
int main() {
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();
return 0;
}
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.
fgetgrent(3),
getgrent(3),
getgrgid(3),
getgrnam(3),
group(5)
