GETPWENT_R(3) Linux Programmer's Manual GETPWENT_R(3)
NAME
getpwent_r, fgetpwent_r - get passwd file entry reentrantly
SYNOPSIS
#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
DESCRIPTION
The functions getpwent_r() and fgetpwent_r() are the reentrant versions
of getpwent(3) and fgetpwent(3). The former reads the next passwd en-
try 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 de-
scribed 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.
RETURN VALUE
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.
ERRORS
ENOENT No more entries.
ERANGE Insufficient buffer space supplied. Try again with larger buf-
fer.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(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.
CONFORMING TO
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);
NOTES
The function getpwent_r() is not really reentrant since it shares the
reading position in the stream with all other threads.
EXAMPLES
#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);
}
SEE ALSO
fgetpwent(3), getpw(3), getpwent(3), getpwnam(3), getpwuid(3), putp-
went(3), passwd(5)
COLOPHON
This page is part of release 5.07 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 2020-06-09 GETPWENT_R(3)