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 correspond-
       ing 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 unwrit-
       ten  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 Technol-
       ogy -- 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)