CODEWITHSUNDEEP
c++macros
Qiufeng54321
Qiufeng54321

Reputation: 179

Function access using macros

This problem is caused when I want to get the address of Functions in Macros after the sign(::).It always has a trailing whitespace which reports an error.

I'm using G++ in Mac OS Mojave i386.

For example, I have the class:

struct A{
  void b();
};

and there's a macro:

#define ACC(name) &A::name

I use this to get the pointer of A::b:

void(*accab)() = ACC(b);

And I will get the error like this:

error: cannot initialize a variable of type 'void (*)()' with an rvalue of type 'void (A::*)()'

After that I tried putting a bracket but I got this:

error: call to non-static member function without an object argument

Is there any way to solve the problem so that the pointer can be gotten by macro?

Upvotes: 1

Views: 165

Answers (1)

P.W
P.W

Reputation: 26800

The type of a pointer to function is different from the type of pointer to member function.

In general, the type of pointer to any member is distinct from the type of a normal pointer.

To make this work you will have declare accab as pointer to member:

void(A::* accab)() = ACC(b);

The C++ standard has a note concerning this:

The type “pointer to member” is distinct from the type “pointer”, that is, a pointer to member is declared only by the pointer to member declarator syntax, and never by the pointer declarator syntax.

Upvotes: 3

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