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Linux 2.6 - man page for fflush (linux section 3posix)

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

       fflush - flush a stream

       #include <stdio.h>

       int fflush(FILE *stream);

       If  stream  points to an output stream or an update stream in which the most recent opera-
       tion 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.

       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.

       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 capabil-
	      ities of the device.

       The following sections are informative.

   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  out-
       put.  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-

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

	      printf("Old password: ");

	      printf("New password: ");


       Data buffered by the system may make determining the validity of the position of the  cur-
       rent 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.


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

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					FFLUSH(P)

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