a question about operator overloading

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I intentionally wrote the following code and it worked!

C++

#include <iostream>
#include <iomanip>
#include <stdlib.h>
using namespace std;

class MaTrix
{
	private:
		int v[10][10],n,m;
	public: 
		friend void operator>>(istream& is, MaTrix &m);
		friend void operator<<(ostream& os, MaTrix m);
		void find_max();
};

//-------------------------------

void operator>>(istream& is, MaTrix &m)
{
	cout<<"Input rows = ";is>>m.n;
	cout<<"Input columns = ";is>>m.m;
	for(int i=0;i<m.n;i++)
		for(int j=0;j<m.m;j++)
		{
			cout<<"Input value v["<<i<<"]["<<j<<"]=";is>>m.v[i][j];
		}
	cout<<"Finish!"<<endl;
}

void operator<<(ostream& os,MaTrix m)
{
	int j;
	for(int i=0;i<m.n;i++)
	{
		for(j=0;j<m.m;j++)
			os<<setw(6)<<m.v[i][j];
		if(j==m.m) os<<endl;
	}
}

void MaTrix::find_max()
{
	int max=v[0][0];
	for(int i=0;i<n;i++)
		for(int j=0;j<m;j++)
			if(v[i][j]>max) max=v[i][j];
	cout<<"Max = "<<max<<endl;
	system("pause");
}

int main()
{
	MaTrix mt;
	cout<<"Input a matrix"<<endl;cin>>mt;
	cout<<"The matrix is : "<<endl;
	cout<<mt;
	mt.find_max();
	return 0;
}

In my lesson the code is :

C++

istream& operator>>(istream& is, MaTrix &m)
{
	cout<<"Input rows = ";is>>m.n;
	cout<<"Input columns = ";is>>m.m;
	for(int i=0;i<m.n;i++)
		for(int j=0;j<m.m;j++)
		{
			cout<<"Input value v["<<i<<"]["<<j<<"]=";is>>m.v[i][j];
		}
	cout<<"Finish!"<<endl;
        return is;
}

ostream& operator<<(ostream& os,MaTrix m)
{
	int j;
	for(int i=0;i<m.n;i++)
	{
		for(j=0;j<m.m;j++)
			os<<setw(6)<<m.v[i][j];
		if(j==m.m) os<<endl;
	}
        return os;
}

Could you tell me how they different? And what is problem if I use the first code?

Posted 17-Dec-13 4:01am

Toan Pham Anh

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Comments

Philippe Mori 19-Dec-13 9:02am

In addition to Solution 1, the prototype of the << operator should be: ostream& operator <<(ostream & os, const Matrix &) to avoid a copy of the object

Toan Pham Anh 9-Jan-14 10:28am

yes, it will make the program run faster!

2 solutions

Solution 2

think bit cin>> and cout<< thats it is belong to #include<iostream.h> same concept.but if it is void then their is no any return type.reason is void mean no any return type.

Posted 17-Dec-13 5:23am

nuke_infer

Comments

Richard MacCutchan 17-Dec-13 12:05pm

You may want to translate that into English.

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Ron Beyer · Accepted Answer · 2013-12-17T04:10:00

Its simple if you think about it. The difference is the return parameters, in C++, people like to write code like:

C++

cout << myvariable << mytext << endl;

Which is only possible if the << overloads on the members return an ostream object. If you return void, you will get a compilation error when you write the above line. You return the ostream object so that you can chain << operators.