C++ #define containing a further # character to stringify the arg - what it means - Argument Preceded by a # Token in a Macro - thanks to Stack Overflow

Argument Preceded by a # Token in a Macro

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#define LINK_ENTITY_TO_CLASS(mapClassName,DLLClassName) \ static CEntityFactory<DLLClassName> mapClassName( #mapClassName ); This is a macro from the Alien Swarm mod for Half-Life 2, meant to be compiled with MSVC. I've never seen an argument preceeded by a # in a macro before, and I'm not sure if this is a MSVC specific thing or just uncommon. What does it mean? c++ macros preprocessor share|edit edited Jul 24 '10 at 0:22 James McNellis 174k20478680 asked Jul 24 '10 at 0:14 Swiss 2,714819

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This is part of both standard C and C++ and is not implementation-specific. The # preprocessing operator stringizes its argument. It takes whatever tokens were passed into the macro for the parameter designated by its operand (in this case, the parameter mapClassName) and makes a string literal out of them. So, for a simple example, #define STRINGIZE(x) # x STRINGIZE(Hello World) // gets replaced with "Hello World" Note that the argument tokens are not macro replaced before they are stringized, so if Hello orWorld were defined as a macro, the result would still be the same. You need to use an extra level of indirection to get the arguments macro replaced (that linked answer discusses the concatenation operator, ##, but applies equally to the stringization operator. share|edit edited Jul 24 '10 at 0:31 answered Jul 24 '10 at 0:18 James McNellis 174k20478680

1   Your answer is right, but I just want to clarify this is a standard part of C preprocessor, and not a MSVC specific thing. –  Swiss Jul 24 '10 at 0:26 @Swiss: Sorry; yes: this is a part of the C language standard. –  James McNellis Jul 24 '10 at 0:31

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