Click here to Skip to main content
12,887,536 members (28,281 online)
Click here to Skip to main content


882 bookmarked
Posted 23 May 2004

Member Function Pointers and the Fastest Possible C++ Delegates

, 5 Apr 2005 CPOL
A comprehensive tutorial on member function pointers, and an implementation of delegates that generates only two ASM opcodes!
#include <stdio.h>
#include "FastDelegate.h"
// Demonstrate the syntax for FastDelegates.
//				-Don Clugston, May 2004.
// It's a really boring example, but it shows the most important cases.

// Declare some functions of varying complexity...
void SimpleStaticFunction(int num, char *str) {
	printf("In SimpleStaticFunction. Num=%d, str = %s\n", num, str);

void SimpleVoidFunction() {
	printf("In SimpleVoidFunction with no parameters.\n");

class CBaseClass {
	char *m_name;
	CBaseClass(char *name) : m_name(name) {};
	void SimpleMemberFunction(int num, char *str) {
		printf("In SimpleMemberFunction in %s. Num=%d, str = %s\n", m_name, num, str);	}
	int SimpleMemberFunctionReturnsInt(int num, char *str) {
		printf("In SimpleMemberFunction in %s. Num=%d, str = %s\n", m_name, num, str); return -1;	}
	void ConstMemberFunction(int num, char *str) const {
		printf("In ConstMemberFunction in %s. Num=%d, str = %s\n", m_name, num, str);	}
	virtual void SimpleVirtualFunction(int num, char *str) {
		printf("In SimpleVirtualFunction in %s. Num=%d, str = %s\n", m_name, num, str);	}
	static void StaticMemberFunction(int num, char *str) {
		printf("In StaticMemberFunction. Num=%d, str =%s\n", num, str);	}

class COtherClass {
	double rubbish; // to ensure this class has non-zero size.
	virtual void UnusedVirtualFunction(void) { }
	virtual void TrickyVirtualFunction(int num, char *str)=0;

class VeryBigClass {
	int letsMakeThingsComplicated[400];

// This declaration ensures that we get a convoluted class heirarchy.
class CDerivedClass : public VeryBigClass, virtual public COtherClass, virtual public CBaseClass
	double m_somemember[8];
	CDerivedClass() : CBaseClass("Base of Derived") { m_somemember[0]=1.2345; }
	void SimpleDerivedFunction(int num, char *str) { printf("In SimpleDerived. num=%d\n", num); }
	virtual void AnotherUnusedVirtualFunction(int num, char *str) {}
	virtual void TrickyVirtualFunction(int num, char *str) {
		printf("In Derived TrickyMemberFunction. Num=%d, str = %s\n", num, str);

using namespace fastdelegate;

int main(void)
	// Delegates with up to 8 parameters are supported.
	// Here's the case for a void function.
	// We declare a delegate and attach it to SimpleVoidFunction()
	printf("-- FastDelegate demo --\nA no-parameter delegate is declared using FastDelegate0\n\n");

	FastDelegate0<> noparameterdelegate(&SimpleVoidFunction);

	noparameterdelegate(); // invoke the delegate - this calls SimpleVoidFunction()

	printf("\n-- Examples using two-parameter delegates (int, char *) --\n\n");

    // By default, the return value is void.
    typedef FastDelegate2<int, char *> MyDelegate;

	// If you want to have a non-void return value, put it at the end.
    typedef FastDelegate2<int, char *, int> IntMyDelegate;

	MyDelegate funclist[12]; // delegates are initialized to empty
	CBaseClass a("Base A");
	CBaseClass b("Base B");
	CDerivedClass d;
	CDerivedClass c;

	IntMyDelegate newdeleg;
    newdeleg = MakeDelegate(&a, &CBaseClass::SimpleMemberFunctionReturnsInt);
	// Binding a simple member function
        funclist[0].bind(&a, &CBaseClass::SimpleMemberFunction);
	// You can also bind static (free) functions
	// and static member functions
	// and const member functions (these only need a const class pointer).		 
        funclist[11].bind( (const CBaseClass *)&a, &CBaseClass::ConstMemberFunction);
        funclist[3].bind( &a, &CBaseClass::ConstMemberFunction);
	// and virtual member functions
        funclist[4].bind(&b, &CBaseClass::SimpleVirtualFunction);

	// You can also use the = operator. For static functions, a fastdelegate
	// looks identical to a simple function pointer.
        funclist[5] = &CBaseClass::StaticMemberFunction;

	// The weird rule about the class of derived member function pointers is avoided.
	// For MSVC, you can use &CDerivedClass::SimpleVirtualFunction here, but DMC will complain.
	// Note that as well as .bind(), you can also use the MakeDelegate()
	// global function.
        funclist[6] = MakeDelegate(&d, &CBaseClass::SimpleVirtualFunction);

	// The worst case is an abstract virtual function of a virtually-derived class
	// with at least one non-virtual base class. This is a VERY obscure situation,
	// which you're unlikely to encounter in the real world.
	// FastDelegate versions prior to 1.3 had problems with this case on VC6.
	// Now, it works without problems on all compilers.
       funclist[7].bind(&c, &CDerivedClass::TrickyVirtualFunction);
	// BUT... in such cases you should be using the base class as an 
	// interface, anyway.
       funclist[8].bind(&c, &COtherClass::TrickyVirtualFunction);
	// Calling a function that was first declared in the derived class is straightforward
        funclist[9] = MakeDelegate(&c, &CDerivedClass::SimpleDerivedFunction);

	// You can also bind directly using the constructor
        MyDelegate dg(&b, &CBaseClass::SimpleVirtualFunction);

	char *msg = "Looking for equal delegate";
	for (int i=0; i<12; i++) {
		printf("%d :", i);
		// The == and != operators are provided
		// Note that they work even for inline functions.
		if (funclist[i]==dg) { msg = "Found equal delegate"; };
		// operator ! can be used to test for an empty delegate
		// You can also use the .empty() member function.
		if (!funclist[i]) {
			printf("Delegate is empty\n");
		} else {
			// Invocation generates optimal assembly code.
			funclist[i](i, msg);
	return 0;

By viewing downloads associated with this article you agree to the Terms of Service and the article's licence.

If a file you wish to view isn't highlighted, and is a text file (not binary), please let us know and we'll add colourisation support for it.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Don Clugston
Germany Germany
I'm an Australian physicist/software engineer living in Leipzig, Germany. I've published papers about windows (the glass kind), semiconductor device physics, environmental philosophy and theology, vacuum systems, and now (at CodeProject) the innards of C++. (Yes, my C.V. is a terrible mess.) I'm a major contributor to the D programming language. I can read New Testament Greek, and can speak German with a dreadful accent.

I have one wife, one son (pictured), and one daughter, who are all much cuter than I am.

"The light shines in the darkness, but the darkness has not overcome it."

You may also be interested in...

Permalink | Advertise | Privacy | Terms of Use | Mobile
Web02 | 2.8.170424.1 | Last Updated 6 Apr 2005
Article Copyright 2004 by Don Clugston
Everything else Copyright © CodeProject, 1999-2017
Layout: fixed | fluid