CODEWITHSUNDEEP
c++macrosconcatenationc-preprocessor
Cray
Cray

Reputation: 2454

## macro argument concatenation not working as I expected

Shouldn't this:

#define MOGSH_CONCAT (x,y) x##y
#define MOGSH_DOUBLE (a,b) MOGSH_CONCAT(a,b)
#define MOGSH_DEFINEPROC (p) MOGSH_DOUBLE(_gt,p) options_dialog::p;

MOGSH_DEFINEPROC(AssignMainForm);

happily expand to:

_gtAssignMainForm options_dialog::AssignMainForm;

Given that _gt is not defined, _gtAssignMainForm is:

typedef void (__stdcall *_gtAssignMainForm)();

and options_dialog is just a class where AssignMainForm is a static member.

Instead, in MSVC9, I get the error:

'a' : undeclared identifier

on the line containing

MOGSH_DEFINEPROC(AssignMainForm);

Upvotes: 0

Views: 1290

Answers (1)

James McNellis
James McNellis

Reputation: 355327

In the definition of a function-like macro there can be no whitespace between the macro name and the ( beginning the parameter list.

#define MOGSH_CONCAT(x,y) x##y 
//                  ^ no whitespace allowed here

As you have it now (with whitespace), MOGSH_CONCAT is an object-like macro with a replacement list of (x,y) x##y, which is why you are getting such strange results.

Upvotes: 3

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