Linux Manual Pages

Free Software * Books

Source Code

Free Media

Linux

GETPWENT_R

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
NOTES
EXAMPLE
SEE ALSO
COLOPHON

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 *fp, struct passwd *pwbuf, char *buf,
size_t buflen, struct passwd **pwbufp);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

getpwent_r(), _BSD_SOURCE || _SVID_SOURCE
fgetpwent_r(): _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 the stream fp.

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.

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 buffer.

CONFORMING TO

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);

NOTES

The function getpwent_r() is not really reentrant since it shares the reading position in the stream with all other threads.

EXAMPLE

#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 411toppm(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);
}

COLOPHON

This page is part of release 3.69 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 http://www.kernel.org/doc/man−pages/.

Opportunity

Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.

Education

Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.