getpwent_r(3) Library Functions Manual getpwent_r(3)
NAME
getpwent_r, fgetpwent_r - get passwd file entry reentrantly
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <pwd.h>
int getpwent_r(struct passwd *restrict pwbuf,
char buf[restrict .buflen], size_t buflen,
struct passwd **restrict pwbufp);
int fgetpwent_r(FILE *restrict stream, struct passwd *restrict pwbuf,
char buf[restrict .buflen], size_t buflen,
struct passwd **restrict 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 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 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 re-
sult 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 *pw-
bufp is NULL.
ERRORS
ENOENT No more entries.
ERANGE Insufficient buffer space supplied. Try again with larger
buffer.
ATTRIBUTES
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 oc-
cur.
VERSIONS
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);
STANDARDS
None.
HISTORY
These functions are done in a style resembling the POSIX version of
functions like getpwnam_r(3).
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 <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#define BUFLEN 4096
int
main(void)
{
struct passwd pw;
struct passwd *pwp;
char buf[BUFLEN];
int i;
setpwent();
while (1) {
i = getpwent_r(&pw, buf, sizeof(buf), &pwp);
if (i)
break;
printf("%s (%jd)\tHOME %s\tSHELL %s\n", pwp->pw_name,
(intmax_t) 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)
Linux man-pages 6.9.1 2024-06-15 getpwent_r(3)
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