getpwent_r, fgetpwent_r - get passwd file entry reentrantly
#include <pwd.h>
int getpwent_r(struct passwd *pwbuf, char *buf,
size_t buflen, struct passwd **pwbufp);
int fgetpwent_r(FILE *stream, struct passwd *pwbuf, char *buf,
size_t buflen, struct passwd **pwbufp);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
getpwent_r(),
Since glibc 2.19:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_BSD_SOURCE || _SVID_SOURCE
fgetpwent_r():
Since glibc 2.19:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_SVID_SOURCE
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
stream.
The
passwd structure is defined in
<pwd.h> as follows:
struct passwd {
char *pw_name; /* username */
char *pw_passwd; /* user password */
uid_t pw_uid; /* user ID */
gid_t pw_gid; /* group ID */
char *pw_gecos; /* user information */
char *pw_dir; /* home directory */
char *pw_shell; /* shell program */
};
For more information about the fields of this structure, see
passwd(5).
The nonreentrant 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.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
getpwent_r () |
Thread safety |
MT-Unsafe race:pwent locale |
fgetpwent_r () |
Thread safety |
MT-Safe |
In the above table,
pwent in
race:pwent signifies that if any of
the functions
setpwent(),
getpwent(),
endpwent(), or
getpwent_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 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.
#define _GNU_SOURCE
#include <pwd.h>
#include <stdio.h>
#define BUFLEN 4096
int
main(void)
{
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();
exit(EXIT_SUCCESS);
}
fgetpwent(3),
getpw(3),
getpwent(3),
getpwnam(3),
getpwuid(3),
putpwent(3),
passwd(5)