Why compiler complants error when compile.

[banbangou]

Anybody could tell me what's wrong with the following code?
It complaints:
13 C:\apps\Dev-Cpp\projects\14\14_1.cpp ISO C++ forbids defining types within return type

Thanks in advance.

#include <iostream>
#include <cstdlib>

using namespace std;

struct vector {
    double x;
    double y;
    
    friend ostream& operator<< (ostream&, vector);
}    

ostream& operator<< (ostream& o, vector a) {
    o << "(" << a.x << "," << a.y << ")" << endl;
    return o;
}    

int main(int argc, char *argv[])
{
    vector v1;
    v1.x = 1;
    v1.y = 1;
    
    cout << v1 << endl;
    
    system("PAUSE");	
    return 0;
}

<< moderator edit: added [code][/code] tags >>

[Dave Sinkula]

There will be ambiguity with your class and std::vector since you are using namespace std.

struct vector
{
   double x;
   double y;

   friend ostream& operator<< (ostream&, vector);
};

If you still want to grab the whole namespace, I think you can disambiguate like this.

friend ostream& operator<< (ostream&, ::vector);

[1o0oBhP]

or in full "std::vector", but there is still a danger that the struct name will cause errors. Easy just to do

namespace my_vector
{
    struct vector // might as well class it
    {
        double x, y;

        friend ostream& operator<< (ostream& out, const vector& v) // I use references but its not compulsory
        {
            out << "(" << a.x << "," << a.y << ")" << endl;
            return out;
        }
    };
}

then in the main just use my_vector::vector v1; instead. This solves any name problems you might have by making your own namespace

[quickhelp]

From what I see you're missing a semicolon after the '}' from your definition of your struct.
hope this helps..