man3/getpwent_r.3

.\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
.\"
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.TH GETPWENT_R 3 2021-03-22 "GNU" "Linux Programmer's Manual"
.SH NAME
getpwent_r, fgetpwent_r \- get passwd file entry reentrantly
.SH SYNOPSIS
.nf
.B #include <pwd.h>
.PP
.BI "int getpwent_r(struct passwd *restrict " pwbuf ,
.BI "               char *restrict " buf ", size_t " buflen ,
.BI "               struct passwd **restrict " pwbufp );
.BI "int fgetpwent_r(FILE *restrict " stream \
", struct passwd *restrict " pwbuf ,
.BI "               char *restrict " buf ", size_t " buflen ,
.BI "               struct passwd **restrict " pwbufp );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR getpwent_r (),
.nf
    Since glibc 2.19:
        _DEFAULT_SOURCE
    Glibc 2.19 and earlier:
        _BSD_SOURCE || _SVID_SOURCE
.fi
.PP
.BR fgetpwent_r ():
.nf
    Since glibc 2.19:
        _DEFAULT_SOURCE
    Glibc 2.19 and earlier:
        _SVID_SOURCE
.fi
.SH DESCRIPTION
The functions
.BR getpwent_r ()
and
.BR fgetpwent_r ()
are the reentrant versions of
.BR getpwent (3)
and
.BR fgetpwent (3).
The former reads the next passwd entry from the stream initialized by
.BR setpwent (3).
The latter reads the next passwd entry from
.IR stream .
.PP
The \fIpasswd\fP structure is defined in
.I <pwd.h>
as follows:
.PP
.in +4n
.EX
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 */
};
.EE
.in
.PP
For more information about the fields of this structure, see
.BR passwd (5).
.PP
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
.I pwbuf
that can hold a \fIstruct passwd\fP.
And next the buffer
.I buf
of size
.I buflen
that can hold additional strings.
The result of these functions, the \fIstruct passwd\fP read from the stream,
is stored in the provided buffer
.IR *pwbuf ,
and a pointer to this \fIstruct passwd\fP is returned in
.IR *pwbufp .
.SH RETURN VALUE
On success, these functions return 0 and
.I *pwbufp
is a pointer to the \fIstruct passwd\fP.
On error, these functions return an error value and
.I *pwbufp
is NULL.
.SH ERRORS
.TP
.B ENOENT
No more entries.
.TP
.B ERANGE
Insufficient buffer space supplied.
Try again with larger buffer.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lb lb lbx
l l l.
Interface	Attribute	Value
T{
.BR getpwent_r ()
T}	Thread safety	T{
MT-Unsafe race:pwent locale
T}
T{
.BR fgetpwent_r ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
In the above table,
.I pwent
in
.I race:pwent
signifies that if any of the functions
.BR setpwent (),
.BR getpwent (),
.BR endpwent (),
or
.BR getpwent_r ()
are used in parallel in different threads of a program,
then data races could occur.
.SH CONFORMING TO
These functions are GNU extensions, done in a style resembling
the POSIX version of functions like
.BR getpwnam_r (3).
Other systems use the prototype
.PP
.in +4n
.EX
struct passwd *
getpwent_r(struct passwd *pwd, char *buf, int buflen);
.EE
.in
.PP
or, better,
.PP
.in +4n
.EX
int
getpwent_r(struct passwd *pwd, char *buf, int buflen,
           FILE **pw_fp);
.EE
.in
.SH NOTES
The function
.BR getpwent_r ()
is not really reentrant since it shares the reading position
in the stream with all other threads.
.SH EXAMPLES
.EX
#define _GNU_SOURCE
#include <pwd.h>
#include <stdio.h>
#include <stdint.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)\etHOME %s\etSHELL %s\en", pwp\->pw_name,
               (intmax_t) pwp\->pw_uid, pwp\->pw_dir, pwp\->pw_shell);
    }
    endpwent();
    exit(EXIT_SUCCESS);
}
.EE
.\" perhaps add error checking - should use strerror_r
.\" #include <errno.h>
.\" #include <stdlib.h>
.\"         if (i) {
.\"               if (i == ENOENT)
.\"                     break;
.\"               printf("getpwent_r: %s", strerror(i));
.\"               exit(EXIT_SUCCESS);
.\"         }
.SH SEE ALSO
.BR fgetpwent (3),
.BR getpw (3),
.BR getpwent (3),
.BR getpwnam (3),
.BR getpwuid (3),
.BR putpwent (3),
.BR passwd (5)