C++Talk.NET

Guest · Posted: Fri Jun 23, 2006 7:50 am Post subject: Callback member functions

Hi, I have two methods A::Conv1 and A::Conv2 that transform coordinates
in two different ways. A::Draw() should take the pointer to one
of these methods as the parameter, and call it.

MSVC++ compiler reports: "term does not evaluate to a function taking
4 arguments". If the CONV type is not a pointer to a member function
taking 4 arguments, then what a hell it is? Smile

GCC reports:
"must use .* or ->* to call pointer-to-member function in conv",
which doesn't helps, too.

How should I call the conv function?

class A {
public:
void Conv1(double X, double Y, int& x, int& y);
void Conv2(double X, double Y, int& x, int& y);
typedef void (A::*CONV)(double, double, int&, int&);
void Draw(CONV conv);
void ReDraw();
A() {
_xscale = 0.5, _yscale = 0.5, _xshift = 100, _yshift = 200;
}
private:
double _xscale, _yscale;
int _xshift, _yshift;
};

void A::Conv1(double X, double Y, int& x, int& y) {
x = (int)(X * _xscale), y = (int)(Y * _yscale);
}
void A::Conv2(double X, double Y, int& x, int& y) {
x = (int)(X * _xscale) + _xshift, y = (int)(Y * _yscale) + _yshift;
}
void A::Draw(CONV conv) {
int x, y;
conv(0.5, 0.5, x, y); // error C2064: term does not evaluate to a
function
}

void A::ReDraw() {
Draw(Conv1);
}

int main() {
A a;
a.ReDraw();
return 0;
}

Victor Bazarov · Guest

kankowski (AT) gmail (DOT) com wrote:

Guest · Posted: Fri Jun 23, 2006 8:25 am Post subject: Re: Callback member functions

I've come up with workaround using friend functions. It does exactly
what I want, but the syntax looks terrible. If someone knows how
to solve the initial problem, I will be very glad to hear you.

#include <stdio.h>
class A;
typedef void (*CONV)(A*, double, double, int&, int&);

class A {
public:
void Draw(CONV conv);
void ReDraw();
A() {
_xscale = 5.0, _yscale = 5.0, _xshift = 100, _yshift = 200;
}
friend void Conv1(A* a, double X, double Y, int& x, int& y);
friend void Conv2(A* a, double X, double Y, int& x, int& y);
private:
double _xscale, _yscale;
int _xshift, _yshift;
};

void Conv1(A* a, double X, double Y, int& x, int& y) {
x = (int)(X * a->_xscale),
y = (int)(Y * a->_yscale);
}
void Conv2(A* a, double X, double Y, int& x, int& y) {
x = (int)(X * a->_xscale) + a->_xshift,
y = (int)(Y * a->_yscale) + a->_yshift;
}
void A::Draw(CONV conv) {
int x, y;
conv(this, 0.5, 0.5, x, y); // error C2064: term does not evaluate to
a function
printf("x=%d y=%d\n", x, y);
}

void A::ReDraw() {
printf("Conv1:\n");
Draw(Conv1);
printf("Conv2:\n");
Draw(Conv2);
}

int main() {
A a;
a.ReDraw();
return 0;
}

Alf P. Steinbach · Guest

* kankowski (AT) gmail (DOT) com:

Phlip · Guest

kankowski wrote:

Guest · Posted: Fri Jun 23, 2006 8:31 am Post subject: Re: Callback member functions

Thank you, it works now. Many thanks!