Member Functions

[jay2tharoc]

First I want to put it out there that yes this is homework and no I'm not asking for it to be done for me :) For my assignment I have to create a class that simulates blocks of memory. I have to write a few member functions and overload some operators. I have +, == and = working as they should but am having some problems with some other aspects of the assignment.

I am tying to overload the << operator. I am having some trouble with it and every example I can find online shows it as a friend function. I haven't seen it as a member function and I haven't figured it out yet so I am not sure how to proceed. To my understanding, a member function needs exactly one argument. I guess if anyone could point me to an example or an example of just the function signature that would help. Thanks for reading.

[Nexius]

Overload it the same way you did the others.

void class_t::operator << (data_t data);

[jay2tharoc]

I tried something similar but I probably screwed up somewhere. Thanks :) I will keep trying.

[ne555]

> To my understanding, a member function needs exactly one argument
Nope, if it is a binary operator then the `left' operand is this (the object that makes the call)
so the signature just ask for one argument.

> I probably screwed up somewhere
Likely, if you show what you did we may help.

[jay2tharoc]

Ok this is what I have. I clearly don't understand something. Hopefully I am at least kind of on track.

This is the error message I get when trying to compile. For line 23 and 30.

Memory.cpp:23:19: error: ‘void Memory::operator<<()’ must take exactly one argument.

 
#include <iostream>

using namespace std;

class Memory {	

	private:
								
		int *arr;
		int size;

	public:
		
		Memory();
		Memory(int size);
		
		void loadArray(int data);
		void dumpArray();
		int getSize();
		Memory operator+(const Memory other);
		Memory& operator=(const Memory other);
		bool operator==(const Memory other);
		void operator<<();	
};

Memory::Memory():Memory(10){};
Memory::Memory(int size): size(size), arr(new int [size]){};


void Memory::operator<<(){
	
	for ( int i = 0; i < this.getSize(); i++ ) {
	
		cout << "Location " << i << " : " << this.arr[i] << endl;
	}
}

bool Memory::operator==(const Memory other){
	
	if ( size != other.size ) return 0;

	for ( int i = 0; i < size; i++ ) {
	
		if ( arr[i] != other.arr[i] ) return 0;
	}
	
	return 1;

}

Memory& Memory::operator=(const Memory other){
	
	for ( int i = 0; i < getSize(); i++){
		
		arr[i] = other.arr[i];
	}

	return *this;
}

Memory Memory::operator+(const Memory other){
	
	Memory result;

	for ( int i = 0; i < getSize(); i++){
	
		result.arr[i] = arr[i] + other.arr[i];
	}
	
	return result;
}

void Memory::dumpArray(){
	
	cout << endl;

	for ( int i = 0; i < getSize(); i++ ) {
	
		cout << "Location " << i << " = " << arr[i] << endl;
	}
}

void Memory::loadArray ( int data ) {
	
	for ( int i = 0; i < getSize() ; i++ ){
		
		arr[i] = data;
	}
}

int Memory::getSize () {
	
	return size;
}

int main(){

	cout << endl;

	Memory a;
	Memory b;
	Memory c;
	Memory d;

	a.loadArray(5);
	b.loadArray(6);
	
	cout << "Dumping c --> c = a + b + a (16)";
	c = a + b + a;
	c.dumpArray();
	
	cout << endl;

	cout << "Dumping d --> d = a (5)";
	d = a;
	d.dumpArray();

	if ( a == b ) cout << "\na is equal to b\n";
	else cout << "\na is NOT equal to b\n";

	//cout << a;
	
	cout << endl;

return 0;
}

[ne555]

cout << a; if that how you intent to use it then it can't be a member function
The message is send to the left object (cout), that's of type ostream.

Either you put it as a member function of ostream, or as a global function
ostream& operator<<( ostream &, const Memory & );

[jay2tharoc]

Ok that's how I was going to do it originally but then I reread the assignment and it said member functions so that's how I was trying to do it.. So I guess my next question is how would I output an array in that way? If it was say a point I could just do something like this I think:

ostream &operator<<( ostream &o, const Point &p) {

return ( o << "X: " << p.x << "Y: " << p.y << endl );
}

Would that be right? I am not sure how I would output an array because then the number of fields would vary depending on size of array.

[ne555]

You need 3 parameters: the stream, the array, the array's size.
But the << is a binary operator (2 parameters)

Alternatives:
_ Use a centinel. Like '\0' for c-strings
_ Use a container that knows its size. Like std::vector
_ Use a `print()' function