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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 (consult 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 underlying 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, Copyright (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.opengroup.org/unix/online.html .

IEEE/The Open Group		     2003			    FFLUSH(3P)
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