PRB: Stringize Operator Fails to Insert Backslashes

ID: Q68143

The information in this article applies to:

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, 16-bit edition, versions 1.0, 1.5
Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 5.0, 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
Version : 5.1 6.0 6.0a 6.0ax 7.0 1.5 1.0 2
Platform : MS-DOS NT WINDOWS
Issue type : kbprb