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



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       fflush - flush a stream

SYNOPSIS
       #include <stdio.h>

       int fflush(FILE *stream);


DESCRIPTION
       If stream points to an output stream or an update stream in which the most recent operation was not input, fflush() shall
       cause any unwritten data for that stream to be written to the file,  and the st_ctime and st_mtime fields of the underly-
       ing file shall be marked for update.

       If stream is a null pointer, fflush() shall perform this flushing action on all streams for which the behavior is defined
       above.

RETURN VALUE
       Upon successful completion, fflush() shall return 0; otherwise, it shall set the error indicator for the  stream,  return
       EOF,  and set errno to indicate the error.

ERRORS
       The fflush() function shall fail if:

       EAGAIN The O_NONBLOCK flag is set for the file descriptor underlying stream and the process would be delayed in the write
              operation.

       EBADF  The file descriptor underlying stream is not valid.

       EFBIG  An attempt was made to write a file that exceeds the maximum file size.

       EFBIG  An attempt was made to write a file that exceeds the process' file size limit.

       EFBIG  The file is a regular file and an attempt was made to write at or beyond the offset maximum  associated  with  the
              corresponding stream.

       EINTR  The fflush() function was interrupted by a signal.

       EIO    The  process  is a member of a background process group attempting to write to its controlling terminal, TOSTOP is
              set, the process is neither ignoring nor blocking SIGTTOU, and the process group of the process is orphaned.  This
              error may also be returned under implementation-defined conditions.

       ENOSPC There was no free space remaining on the device containing the file.

       EPIPE  An  attempt is made to write to a pipe or FIFO that is not open for reading by any process. A SIGPIPE signal shall
              also be sent to the thread.


       The fflush() function may fail if:

       ENXIO  A request was made of a nonexistent device, or the request was outside the capabilities of the device.


       The following sections are informative.

EXAMPLES
   Sending Prompts to Standard Output
       The following example uses printf() calls to print a series of prompts for information the user must enter from  standard
       input.  The  fflush() calls force the output to standard output. The fflush() function is used because standard output is
       usually buffered and the prompt may not immediately be printed on the output or terminal. The gets() calls  read  strings
       from standard input and place the results in variables, for use later in the program.


              #include <stdio.h>
              ...
              char user[100];
              char oldpasswd[100];
              char newpasswd[100];
              ...
              printf("User name: ");
              fflush(stdout);
              gets(user);


              printf("Old password: ");
              fflush(stdout);
              gets(oldpasswd);


              printf("New password: ");
              fflush(stdout);
              gets(newpasswd);
              ...

APPLICATION USAGE
       None.

RATIONALE
       Data buffered by the system may make determining the validity of the position of the current file descriptor impractical.
       Thus, enforcing the repositioning of the file descriptor after fflush() on streams open for read()  is  not  mandated  by
       IEEE Std 1003.1-2001.

FUTURE DIRECTIONS
       None.

SEE ALSO
       getrlimit(), ulimit(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdio.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    FFLUSH(3P)