Thread: overloading operator help

k, this board is my only available "lab" for a univeristy level course, so please help if u can...

i am pretty sure i simply do not understand classes yet, but my stupid assignment is asking me to overload operators and i just cant make the compiler happy. after following the instrcutor's example, i get stuck with odd compiler errors that dont make any sense (go figure).

if anyone can point out what i am doing wrong, i would appreciate it...

Code:

#include <iostream.h>

class point
{
	private:
		float x;
	public: 
		point()	{ cout<<"Enter a fraction: "; cin>>x; };
		point operator +(point a, point b); // point a, point b
};
float point operator +(point a, point b)
{
		point result;
		result.x=a.x+b.x;
		return result;
}
void main()
{
	point a;
	point b;
	a.read();
	b.read();
	point r1=a+b;
}

Code:

fractions_source.cpp(9) : error C2804: binary 'operator +' has too many parameters
fractions_source.cpp(11) : error C2143: syntax error : missing ';' before '+'
fractions_source.cpp(11) : fatal error C1004: unexpected end of file found

Code:

float point operator +(point a, point b)

should be

Code:

point operator +(point a, point b)

and

Code:

point operator +(point a, point b); // point a, point b

should be

Code:

friend point operator +(point a, point b); // point a, point b

because the function returns a point, not a float, and because the function should not be part of the point class.

that worked, thanx jlou

230? i'm only in 131...

i hope u have a lab, cuz my school feels it's unnecessary for some odd reason

Your example code requires you to "Enter a fraction" when calling the operator+ function because of the temp result object that is created. This input is thrown away in this case and probably should not be a part of your constructor code, which I suspect may be the case since you mention a read function but do not include that code in your sample.

Here is one more way for comparisons sake that does things a little differently, I have added the friend ostream& operator<< to make output easy and also the read function:

Code:

#include <iostream>  // The iostream.h header is deprecated, use this newer version
// Due to the above header change you will also need to deal with namespaces,
// for this simple example's sake just add this following line
using namespace std;

class point
{
private:
    float x;
public: 
    point()	{}
    void read() { cout<<"Enter a fraction: "; cin>>x; }  // Moved from constructor
    point operator +(const point& b);
    friend ostream& operator<<(ostream& os, const point& pt);
};

ostream& operator<<(ostream& os, const point& pt)
{
    return os << pt.x << endl;
}

point point::operator +(const point& b)
{
    point result;
    result.x = x + b.x;
    return result;
}

int main() // main returns an int always
{
    point a;
    point b;
    a.read();
    b.read();
    point r1=a+b;
    cout << a << b << r1;
    return 0;
}

Example output:

Code:

Enter a fraction: 6.7
Enter a fraction: 4.9
6.7
4.9
11.6

hk_mp5kpdw---In your example of overloading the + operator as a member function of the class, I believe you also need to add a public accessor function. This is because the desired member variable of the parameter you are passing to the current objects operator is declared with private access and therefore is not available to other objects of the class directly.

Also, since you don't have any newlines, explicitly or implicitly by use of keyword endl, the output will all be on one line rather than on separate lines as posted. Not that that has anything to do with operator overloading, but...

Originally Posted by elad

hk_mp5kpdw---In your example of overloading the + operator as a member function of the class, I believe you also need to add a public accessor function. This is because the desired member variable of the parameter you are passing to the current objects operator is declared with private access and therefore is not available to other objects of the class directly.

Works for me. I tested the code out as posted using MS Visual Studio and it ran as shown in the example output. As a member function of the point class, operator+ can access the member variables of that class. A public accessor function would work but I don't think it is needed.

Originally Posted by elad

Also, since you don't have any newlines, explicitly or implicitly by use of keyword endl, the output will all be on one line rather than on separate lines as posted. Not that that has anything to do with operator overloading, but...

Code:

ostream& operator<<(ostream& os, const point& pt)
{
    return os << pt.x << endl;
}
...
cout << a << b << r1;

The endl is there, just not where you thought it was.