Originální popis anglicky:
getpwent_r, fgetpwent_r - get passwd file entry reentrantly
Návod, kniha: Linux Programmer's Manual
#define _GNU_SOURCE
#include <pwd.h>
int getpwent_r(struct passwd *pwbuf, char *buf,
size_t buflen, struct passwd **pwbufp);
int fgetpwent_r(FILE *fp, struct passwd *pwbuf, char *buf,
size_t buflen, struct passwd **pwbufp);
The functions
getpwent_r() and
fgetpwent_r() are the reentrant
versions of
getpwent(3) and
fgetpwent(3). The former reads the
next passwd entry from the stream initialized by
setpwent(3). The
latter reads the next passwd entry from the stream
fp given as
parameter.
The
passwd structure is defined in
<pwd.h> as follows:
struct passwd {
char *pw_name; /* user name */
char *pw_passwd; /* user password */
uid_t pw_uid; /* user id */
gid_t pw_gid; /* group id */
char *pw_gecos; /* real name */
char *pw_dir; /* home directory */
char *pw_shell; /* shell program */
};
The non-reentrant functions return a pointer to static storage, where this
static storage contains further pointers to user name, password, gecos field,
home directory and shell. The reentrant functions described here return all of
that in caller-provided buffers. First of all there is the buffer
pwbuf
that can hold a struct passwd. And next the buffer
buf of size
buflen that can hold additional strings. The result of these functions,
the struct passwd read from the stream, is stored in the provided buffer
*
pwbuf, and a pointer to this struct passwd is returned in
*
pwbufp.
On success, these functions return 0 and *
pwbufp is a pointer to the
struct passwd. On error, these functions return an error value and
*
pwbufp is NULL.
- ENOENT
- No more entries.
- ERANGE
- Insufficient buffer space supplied. Try again with larger
buffer.
#define _GNU_SOURCE
#include <pwd.h>
#include <stdio.h>
#define BUFLEN 4096
int main() {
struct passwd pw, *pwp;
char buf[BUFLEN];
int i;
setpwent();
while (1) {
i = getpwent_r(&pw, buf, BUFLEN, &pwp);
if (i)
break;
printf("%s (%d)\tHOME %s\tSHELL %s\n",
pwp->pw_name, pwp->pw_uid,
pwp->pw_dir, pwp->pw_shell);
}
endpwent();
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 passwd *
getpwent_r(struct passwd *pwd, char *buf, int buflen);
or, better,
int
getpwent_r(struct passwd *pwd, char *buf, int buflen,
FILE **pw_fp);
The function
getpwent_r() is not really reentrant since it shares the
reading position in the stream with all other threads.
fgetpwent(3),
getpw(3),
getpwent(3),
getpwnam(3),
getpwuid(3),
putpwent(3),
passwd(5)
