Q122442: PRB: stdout/stderr May Not Be In Sync When Using Redirection

Article: Q122442
Product(s): Microsoft C Compiler
Version(s): 1.5,1.51,2.0,2.1,4.0,5.0,6.0
Operating System(s): 
Keyword(s): kbCRT kbVC kbVC150 kbVC151 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600
Last Modified: 11-FEB-2002

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The information in this article applies to:

- The C Run-Time (CRT), included with:
   - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.5, 1.51 
   - Microsoft Visual C++, 32-bit Editions, versions 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 
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SYMPTOMS
========

When the standard output and error streams are redirected or piped, console
application output may not be serialized. This can result in unexpected output.

CAUSE
=====

Although devices as serialized by default, the current Microsoft CRT
implementation does not treat pipes as if they were devices (due to the
potentially high overhead--added code--of doing so.) Thus, if stderr and stdout
refer to the same file or device, and output is redirected with a pipe, the
output will not be serialized.

STATUS
======

This behavior is by design. The potential for slow execution currently outweighs
the effort necessary to implement pipes such that they are treated as devices.

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

To demonstrate this behavior, build and run the sample code (TEST.C) below. If
it is executed from an MS-DOS or Windows NT command prompt, the following output
is generated:

 c:\>test
 hello world (stdout)
 hello world (stderr)
 hello world (stdout)
 hello world (stderr)

However, if the output is piped with the MORE command, it will not be serialized,
as follows:

 c:\>test | more
 hello world (stderr)
 hello world (stderr)
 hello world (stdout)
 hello world (stdout)

Sample Code
-----------

     /* Compile options needed: none
     /*

     /* TEST.C */ 

     #include <stdio.h>

     int main(void)
     {
       printf ( "Hello world (stdout)\n" );
       fprintf ( stderr, "Hello world (stderr)\n" );
       printf ( "Hello world (stdout)\n" );
       fprintf ( stderr, "Hello world (stderr)\n" );
     }

Additional query words:

======================================================================
Keywords          : kbCRT kbVC kbVC150 kbVC151 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600 
Technology        : kbVCsearch kbAudDeveloper kbCRT
Version           : :1.5,1.51,2.0,2.1,4.0,5.0,6.0
Issue type        : kbprb

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