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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 dif-
       fer (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  pro-
              cess 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 pro-
       gram.


              #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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, 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)