Q68143

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Q68143: Stringize Operator Fails to Insert Backslashes

Article: Q68143
Version(s): 5.10 6.00 6.00a | 5.10 6.00 6.00a
Operating System: MS-DOS          | OS/2
Flags: ENDUSER | buglist 5.10 buglist6.00 buglist6.00a s_quickc
Last Modified: 31-JAN-1991

The stringizing operator is used only with the arguments of macros. 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.

Below are some sample macros that use the stringize 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:

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

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 (missing ')'?)

Expected Output:

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

Microsoft has confirmed this to be a problem in C versions 5.10, 6.00,
and 6.00a and QuickC versions 2.00, 2.01, 2.50, and 2.51 (buglist2.00,
buglist2.01, buglist2.50, and buglist2.51). We are researching this
problem and will post new information here as it becomes available.