Variable name from macro argument

Question

I'd like to do something like this:

class SomeClass { };

GENERATE_FUNTION(SomeClass)

The GENERATE_FUNCTION macro I'd like to define a function whose name is to be determined by the macro argument. In this case, I'd like it to define a function func_SomeClass. How can that be done?

K-ballo · Accepted Answer · 2011-09-26 21:59:22Z

46

#define GENERATE_FUNCTION(Argument) void func_##Argument(){ ... }

More information here: http://en.wikipedia.org/wiki/C_preprocessor#Token_concatenation

answered Sep 26, 2011 at 21:59

K-ballo

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4 Comments

Mooing Duck Over a year ago

Keep in mind if you give it a macro as a parameter, there's more preprocessor magic involved to make it work.

K-ballo Over a year ago

@Mooing Duck: Yes, an extra level of indirection to actually evaluate the Argument before pasting. However that does not seem to be the OP case.

qed Over a year ago

What if I don't want the func_ part?

ReinstateMonica3167040 Over a year ago

@qed If you don't want the func_ part to be there at all, you could just do #define GENERATE_FUNCTION(Argument) void Argument() { ... }

Dmitri · Accepted Answer · 2011-09-26 22:29:10Z

10

As everyone says, you can use token pasting to build the name in your macro, by placing ## where needed to join tokens together.

If the preprocessor supports variadic macros, you can include the return type and parameter list too:

#define GENERATE_FUNCTION(RET,NAM,...) RET func_##NAM(__VA_ARGS__)

..so, for example:

GENERATE_FUNCTION(int,SomeClass,int val)

..would expand to:

int func_SomeClass(int val)

answered Sep 26, 2011 at 22:29

Dmitri

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Comments

user142162 · Accepted Answer · 2011-09-26 21:59:20Z

4

#define GENERATE_FUNCTION(class_name) func_##class_name##

answered Sep 26, 2011 at 21:59

user142162

2 Comments

Silicomancer Over a year ago

What does the final ## do?

Purple Ice Over a year ago

Apparently makes it not work at all :) (GCC via mingw64)

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