Manpages - endpwent.3p
Table of Contents
PROLOG
This manual page is part of the POSIX Programmer’s Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAME
endpwent, getpwent, setpwent — user database functions
SYNOPSIS
#include <pwd.h> void endpwent(void); struct passwd *getpwent(void); void setpwent(void);
DESCRIPTION
These functions shall retrieve information about users.
The /getpwent/() function shall return a pointer to a structure containing the broken-out fields of an entry in the user database. Each entry in the user database contains a passwd structure. If the user database is not already open, /getpwent/() shall open it and return a pointer to a passwd structure containing the first entry in the database. Thereafter, it shall return a pointer to a passwd structure containing the next entry in the user database. Successive calls can be used to search the entire user database.
If an end-of-file or an error is encountered on reading, /getpwent/() shall return a null pointer.
An implementation that provides extended security controls may impose further implementation-defined restrictions on accessing the user database. In particular, the system may deny the existence of some or all of the user database entries associated with users other than the caller.
The /setpwent/() function shall rewind the user database so that the next /getpwent/() call returns the first entry, allowing repeated searches.
The /endpwent/() function shall close the user database.
The setpwent/() and /endpwent/() functions shall not change the setting of /errno if successful.
On error, the setpwent/() and /endpwent/() functions shall set /errno to indicate the error.
Since no value is returned by the /setpwent/() and /endpwent/() functions, an application wishing to check for error situations should set errno to 0, then call the function, then check errno.
These functions need not be thread-safe.
RETURN VALUE
On successful completion, /getpwent/() shall return a pointer to a passwd structure. On end-of-file, getpwent/() shall return a null pointer and shall not change the setting of /errno. On error, getpwent/() shall return a null pointer and /errno shall be set to indicate the error.
The application shall not modify the structure to which the return value points, nor any storage areas pointed to by pointers within the structure. The returned pointer, and pointers within the structure, might be invalidated or the structure or the storage areas might be overwritten by a subsequent call to /getpwuid/(), /getpwnam/(), or /getpwent/(). The returned pointer, and pointers within the structure, might also be invalidated if the calling thread is terminated.
ERRORS
These functions may fail if:
- EINTR
- A signal was caught during the operation.
- EIO
- An I/O error has occurred.
In addition, /getpwent/() and /setpwent/() may fail if:
- EMFILE
- All file descriptors available to the process are currently open.
- ENFILE
- The maximum allowable number of files is currently open in the system.
The following sections are informative.
EXAMPLES
Searching the User Database
The following example uses the /getpwent/() function to get successive entries in the user database, returning a pointer to a passwd structure that contains information about each user. The call to /endpwent/() closes the user database and cleans up.
#include <pwd.h>
#include <stdio.h>
void printname(uid_t uid)
{
struct passwd *pwd;
setpwent();
while((pwd = getpwent()) != NULL) {
if (pwd->pw_uid == uid) {
printf("name=%s\n",pwd->pw_name);
break;
}
}
endpwent();
}
APPLICATION USAGE
These functions are provided due to their historical usage. Applications should avoid dependencies on fields in the password database, whether the database is a single file, or where in the file system name space the database resides. Applications should use /getpwuid/() whenever possible because it avoids these dependencies.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
/endgrent ( )/, /getlogin ( )/, /getpwnam ( )/, /getpwuid ( )/
The Base Definitions volume of POSIX.1‐2017, <pwd.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology – Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .