Q68143: PRB: Stringize Operator Fails to Insert Backslashes

Article: Q68143
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,2.0,2.1,4.0,5.0,6.0
Operating System(s): 
Keyword(s): kbLangC kbVC100 kbVC150 kbVC200 kbVC210 kbVC400 kbVC500
Last Modified: 14-NOV-2001

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

- Microsoft C/C++ compiler for MS-DOS 
- Microsoft Visual C++, versions 1.0, 1.5, 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 
-------------------------------------------------------------------------------

SYMPTOMS
========

The Microsoft C and C/C++ compilers support the use of the stringizing
preprocessor operator only in macros that take arguments. If a # precedes a
formal parameter in the definition of a macro, the actual argument is enclosed
in double quotation marks and treated as a string when the macro is expanded.

If the argument contains characters that normally must be preceded by a backslash
(\) when appearing in a string (such as " or \), the backslash should be
automatically inserted. However, there are many cases where the preprocessor
fails to do this.

STATUS
======

This behavior is by design.

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

Following are some sample macros that use the stringizing operator. They are
followed by a line showing the incorrect preprocessor output (compiling with /P)
and the output that was expected.

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

Example 1:

  #define print_filename(x) printf(#x);

  main()
  {
   print_filename(d:\test\sscanf.c)
  }

Preprocessor Output:

  printf("d:\test\sscanf.c");

Expected Output:

  printf("d:\\test\\sscanf.c");

Example 2:

  #define print_filename(x) printf(#x);

  main()
  {
     print_filename(This: \" prints an escaped double quote mark)
  }

Preprocessor Output for C Compiler version 6.0:

  printf("This: \\" prints an escaped double quote mark")

Preprocessor Output for C/C++ Compilers, Versions 7.0 and above:

  error C2001: newline in constant
  fatal error C1057: unexpected end-of-file in macro expansion

Expected Output:

  printf("This: \\\" prints an escaped double quote mark")

Example 3:

  #define print_stuff(x) printf(#x);

  main()
  {
     print_stuff(I am printing a quote: ")
  }

Preprocessor Output:

  error C2001: newline in constant
  fatal error C1057: unexpected end-of-file in macro expansion

Expected Output:

  printf("I am printing a quote: \"");

Additional query words:

======================================================================
Keywords          : kbLangC kbVC100 kbVC150 kbVC200 kbVC210 kbVC400 kbVC500 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbZNotKeyword8 kbvc150 kbvc100 kbZNotKeyword3 kbVC500 kbVC600 kbVC200 kbVC210 kbVC32bitSearch kbVC500Search
Version           : :1.0,1.5,2.0,2.1,4.0,5.0,6.0
Issue type        : kbprb

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

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.