Article ID: 122442
Article Last Modified on 8/5/2005
APPLIES TO
- The C Run-Time (CRT), when used with:
- Microsoft Visual C++ 1.5 Professional Edition
- Microsoft Visual C++ 1.51
- Microsoft Visual C++ 2.0 Professional Edition
- Microsoft Visual C++ 2.1
- Microsoft Visual C++ 4.0 Standard Edition
- Microsoft Visual C++ 5.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 5.0 Professional Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition
This article was previously published under Q122442
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" );
}
Keywords: kbtshoot kbprb KB122442
