endpwent(3p) — Linux manual page

ENDPWENT(3P)            POSIX Programmer's Manual           ENDPWENT(3P)

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(3p), getlogin(3p), getpwnam(3p), getpwuid(3p)

       The Base Definitions volume of POSIX.1‐2017, pwd.h(0p)

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 .

IEEE/The Open Group               2017                      ENDPWENT(3P)

Pages that refer to this page: pwd.h(0p), endgrent(3p), getpwent(3p), setpwent(3p)

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