Q94227: INFO: Output Stream cout Is Buffered

Article: Q94227
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,1.51,1.52,2.0,2.1,4.0,5.0,6.0
Operating System(s): 
Keyword(s): kbLangCPP kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600
Last Modified: 13-NOV-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft C/C++ for MS-DOS 
- Microsoft Visual C++, versions 1.0, 1.5, 1.51, 1.52, 2.0, 2.1, 4.0 
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
-------------------------------------------------------------------------------


SUMMARY
=======

In an application developed with Microsoft C/C++, the cout stream is buffered.
In other words, information sent to the cout stream does not appear on the
screen until its buffers are flushed. For Visual C++ versions 4.2 and 5.0, this
behavior only occurs when using the old iostream libraries. There are four
methods to flush the cout buffer, as follows:

- Use the endl manipulator to insert a newline character into the output stream
  and flush the buffer. Use the insertion operator with the endl manipulator,
  as follows:

  cout << ... << endl;

- Use the flush member function in the ostream class or the flush manipulator.
  The flush manipulator does not insert a newline character into the stream
  before it flushes the buffer. To call the flush member function, use code
  similar to the following:

  cout.flush();

  Use the insertion operator with the flush manipulator as follows:

  cout << ... << flush;

- Read from the cin stream or write to the cerr or clog streams. Because these
  objects share the buffer with cout, each flushes the contents of the buffer
  before making any changes to it.

- Exit the program to flush all buffers currently in use.

MORE INFORMATION
================

Because cout is buffered, text that the application creates is not immediately
displayed on the screen. In some circumstances, this behavior might be
misinterpreted as an error in cout. For an example of an application that
determines when to flush the cout buffer, see pages 377- 378 of the Microsoft
C/C++ "Class Libraries User's Guide" for version 7.0.

For more information on flushing the cout stream with the endl manipulator,
please see the following article in the Microsoft Knowledge Base:

  Q83081 INFO: Endl Flushes the cout Buffer Immediately Upon Execution

Additional query words:

======================================================================
Keywords          : kbLangCPP kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbZNotKeyword8 kbvc150 kbvc100 kbZNotKeyword3 kbVC500 kbVC600 kbVC151 kbVC200 kbVC210 kbVC32bitSearch kbVC152 kbVC500Search
Version           : :1.0,1.5,1.51,1.52,2.0,2.1,4.0,5.0,6.0
Issue type        : kbinfo

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.