Why compiler complants error when compile.
 

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 >>

Re: Why compiler complants error when compile.
 

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);

Re: Why compiler complants error when compile.
 

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

Re: Why compiler complants error when compile.
 

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