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:
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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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