Operator overloading problem

QWERTYman (255)

Upon attempting an operator overloadulation (yes, I know, not a word), I get an error stating that

ostream & operator<<(ostream &, nation) must take exactly one argument

I know what this means (I think), but I have no idea how to fix it. Also, my other error arose due to this, that there is no match for operator<<() in std::cout << yours. Any ideas? Here is my code:

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#include <iostream>
using namespace std;

class nation
{
    string name;
    long population;
    long size;
    bool borders_water;
    bool island;
    public:
nation(string n, int p = 1000, int s = 1000, bool b = true, bool i = false)
    {
        name = n;
        population = p;
        size = s;
        borders_water = b;
        island = i;
    }
void setpop(int p)
    {
        population = p;
    }
void setsize(int s)
    {
        size = s;
    }
void addpop(int p)
    {
        population += p;
    }
void addsize(int s)
    {
        size += s;
    }
ostream & operator<<(ostream & os, nation obj)
{
        os << obj.name << endl << "Population: " << obj.population << endl << "Area: " << obj.size << endl << "It does";
       if(!obj.borders_water)
    {
        os << "n't border water\n";
    }
        else
    {
        os << " border water\nIt is";
        if(!obj.island)
        {
            os << "n't";
        }
        os << " an island";
    }
    return os;
}
};

int main()
{
    cout << "Name of your nation: ";
    string name;
    getline(cin, name);
    cout << "Population: ";
    long pop;
    cin >> pop;
    cout << "Area: ";
    long ar;
    cin >> ar;
    cout << "Does it border water? [0 for false, 1 for true]: ";
    bool b;
    cin >> b;
    bool i;
    if(b == 1){
    cout << "Is it an island? [0 for false, 1 for true]: ";
    cin >> i;}
    else
    i == false;
    nation yours(name, pop, ar, b, i);
    cout << yours;
    cin.get();
    cin.get();
    return 0;
}

helios (1518)

I must admit I'm not exactly an expert at dealing with streams like this, but it's just that. operator<< only takes one parameter, which is the right hand operand (the type of the left hand is determined by the class that defined the operator).

mahlerfive (117)

Add 'friend' in front:


friend ostream & operator<<(ostream & os, nation obj)

jsmith (958)

And pass the nation object by const reference, please.


friend ostream& operator<<( ostream& os, nation const& obj ) { /*...*/ }

Umz (153)

I'm no pro with overloading operators but it might just be better to do it externally instead of making it a friend of the class nation.

Also another way to format output is to use a member function that takes a ostream& object

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void display(ostream& out) {
out << name << endl << "Population: " << population

etc.

Then when you want to display it overload the operator<< do externally:

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ostream& operator<<(ostream& o, nation& n) {
n.display(o);
return o;
}

Then just use the overloaded in the main function with the object


cout << nation;

Last edited on

QWERTYman (255)

Mahlerfive's solution worked, sorry for not saying so earlier.

Thanks.

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