PRB: When Compiling with /P, Errors Are Directed to STDERR (68834)

The information in this article applies to:

Microsoft C for MS-DOS
Microsoft C for OS/2
Microsoft Visual C++ for Windows, 16-bit edition 1.0
Microsoft Visual C++ for Windows, 16-bit edition 1.5
Microsoft Visual C++ for Windows, 16-bit edition 1.51
Microsoft Visual C++, 32-bit Editions 1.0
Microsoft Visual C++, 32-bit Editions 2.0
Microsoft Visual C++, 32-bit Editions 2.1
Microsoft Visual C++, 32-bit Editions 4.0
Microsoft Visual C++, 32-bit Editions 5.0
Microsoft Visual C++, 32-bit Editions 6.0

This article was previously published under Q68834

SYMPTOMS

The Microsoft C compiler can create a preprocessor listing by compiling with the /P option. If this option is used and output is redirected to a file, preprocessor error messages that are generated will go to the screen and not to the specified file.

CAUSE

This results from preprocessor errors being directed to STDERR, rather than STDOUT.

This behavior is by design. Normally the output of the compiler is syntax errors and warnings. However, when you are using the preprocessing options, the output from the compiler is the preprocessed output. Allowing preprocessor errors to be redirected would result in the errors and warnings appearing in the preprocessed file.

RESOLUTION

To resolve the problem, redirect STDERR to the file where you want the error messages to go. This can been done in MS-DOS by using a utility, such as ERROUT.EXE, which comes with C 5.1. Under OS/2 or Windows NT, the STDERR output can be redirected to a file by specifying the handle for STDERR, which is 2, followed by ">" and then the name of the file.

MORE INFORMATION

The examples below demonstrate the syntax. For MS-DOS, using ERROUT.EXE, use the following:

   ERROUT /f err.txt cl /P example.c

For OS/2, Windows NT, or Windows 2000, use the following:

CL /P 2>outfile.txt example.c

Modification Type:	Minor	Last Reviewed:	7/5/2005
Keywords:	kbCompiler kbprb KB68834