PRB: Stringize Operator Fails to Insert Backslashes

• Microsoft C compiler for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax
• Microsoft C/C++ compiler for MS-DOS, version 7.0
• Microsoft Visual C++ for Windows, versions 1.0, 1.5
• Microsoft Visual C++, 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 5.0

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)
    }

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

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

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

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

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

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

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

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

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

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