Visual C++ errors C3867 and C2664

Question

#define UCHAR unsigned char

typedef bool (*FUNC)(UCHAR uc1, UCHAR uc2);
typedef void(*PF)(FUNC, UCHAR*);
PF    Assign;

class Class  {
    private:
       UCHAR buf[32];
       bool func(UCHAR c1, UCHAR c2)  { }

    public:
       Class::Class(void)  {
          Assign( func, buf );         // <<< Microsoft VC++ error C3867
       }

       Class::~Class()  { }
};

error C3867: 'Class::func': function call missing argument list; use '&Class::func' to create a pointer to member

If I try the suggestion in the error message above

Assign( &Class::func, buf ); // <<< Microsoft VC++ error C2664

I get this error:

error C2664: 'void (FUNC,unsigned char *)' : cannot convert parameter 1 from 'bool (__thiscall Class::* )(unsigned char,unsigned char)' to 'FUNC' There is no context in which this conversion is possible

Without changing anything else how can I get this Assign() function to compile? These typedefs are from a library that I need to interface with.

Answer 1

The type-aliases FUNC and PF are not a member function pointers, and can only be used to point to static member functions. The reason being that all non-static member functions have an implicit first argument for the this pointer.

If you need generic function "pointers" you should look into std::function:

typedef std::function<bool(UCHAR uc1, UCHAR uc2)> FUNC;
typedef std::function<void(FUNC, UCHAR*)> PF;
PF    Assign;

Class::Class(void)  {
    Assign( std::bind(&Class::func, *this), buf );
}

Answer 2

func is a non-static member function, so its type is bool (Class::*)(UCHAR, UCHAR), while Assign requires bool (*)(UCHAR, UCHAR). You cannot convert a non-static member function to a non-member function.

To be able to pass func into Assign, you'll have to make func static.