issues with overloading the output operator

[momotaro]

am trying to overload my output operator but it gives me these errors:

error C2143: syntax error : missing ';' before '&'

error C2433: 'ostream' : 'friend' not permitted on data declarations

error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

error C2061: syntax error : identifier 'ostream'

error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

error C2805: binary 'operator <<' has too few parameters

here my prototype function in the header file:

friend ostream& operator<<(ostream &out, MyPoint &p);

and here is my implementation:

ostream& operator<<(ostream &out, MyPoint &m)
{
    return out<< "X = " <<m.getAbs() << "Y = " <<m.getOrd() <<endl;
}

[Oralloy]

Try dropping the keyword friend from your declaration.

The reason is that your function is just that, a function; it is not a method of any class.

[momotaro]

thank's Oralloy but this is not how we overload the output stream operator!
if you have any other suggestion please feel free.
PS: the keyword friend here is mandatory !

[weaknessforcats]

From your posting, Oralloy is correct and the friend keyword is in error. A friend can only occur inside a class declaration and what you have posted is not inside a class declaration.

Then, the compiler has a problem with the &. That means that by the time the compiler reached an & it was in trouble. Most likely, either ostream or MyPoint has no been declared before being used. Check that yu have included the appropriate headers.

[Oralloy]

momotaro,

Look at the bottom of this page for some template examples of what you're trying to implement.

Good Luck!

[momotaro]

when I posted I assumed that the line of code being in a class declaration is obvious my bad here is my hole code:

#include "Vector.h"
class MyPoint
{
 
private:
    double abs;
    double ord;
 
public:
    MyPoint(double x=0, double y=0);
    double getAbs(void);
    void setAbs(double);
    double getOrd(void);
    void setOrd(double);
    bool coincide(MyPoint);
    static bool coincide_static(MyPoint, MyPoint);
    MyPoint operator+(MyPoint);
    MyPoint operator++();
    MyPoint operator++(int);
    void affiche();
    friend bool coincide_friend(MyPoint, MyPoint);
    MyPoint translate(Vector v);
    MyPoint multiple(Vector v);
    friend ostream& operator<<(ostream &out, MyPoint &p);
};

[Oralloy]

momotaro,

If I understand your code, ostream isn't declared in your module, unless it's coming indirectly from Vector.h

You can cheat and use a foreward reference of the sort

class std::ostream;

Or, you can simply include the appropriate C++ header at the top of your file.

Luck!

[momotaro]

It was the first thing I tried out but no chance still giving me the same error could it be a bug in the compiler or something?? I've read that somewhere...
thank's in advance

[Oralloy]

momotaro,

Why does the overloaded operator need to be declared a friend of your class, anyway? It only uses the public interface, from what I see.

On the other hand, you might be experiencing a problem with usage. This is microsoft, and I don't remember if they normally import the std namespace into the root namespace or not.

If you #include <iostream>, instead of #include <iostream.h>, it might help.

Also, you might change the friend declaration as such:

    friend std::ostream& operator<<(std::ostream &out, MyPoint &p);

Cheers!

[weaknessforcats]

You can't use ostream& unless you have declared an ostream class. That means this won't work:

class ostream;

A forward reference is OK when you need a pointer to an object but for a reference to an object the compiler needs the full class declaration to insure you use the reference correctly.

#include <iostream>

[Oralloy]

weaknessforcats,

I did not realize that. I thought a forward reference was acceptable, assuming a correct type match and none of the class details were accessed in the referencing code. (in this case, the friend declaration)

Good to learn something.

Thank You.

[momotaro]

If I take out the keyword friend gives me another error:
too many parameters
PS: iostream is included but still giving me ostream undefined

driving me crazy :(

thx in advance

[Oralloy]

momotaro,

did you try using std::ostream, instead?

[momotaro]

yes! and now without the keyword friend its telling me too many param in the header and too few in the definition file
:D how is it even possible
thx in advance

[Oralloy]

momotaro,

The iostreams are declared and defined in the std:: namespace.

What is getting you is how microsloth deals with namespaces. I have been bitten by this problem before, and if you include <iostream.h> you get different namespace usage than if you use <iostream>.

If you don't know what a namespace is, think of it as a class where all methods are public-static, and no attributes. Obviously, one can't instantiate a namespace. All it is is a means of isolating related functions and data from other packages. You will sometimes find them in larger projects that break down into logical sub-components. I'm afraid that most developers seem to consider them a pain, rather than the utility that they are.

All that said, I still don't understand why you need that friend declaration in your class at all.

Good Luck!

[momotaro]

lets say I took it out!
now my overloading method is as follows: (assuming imports are correct)

std::ostream& operator<<(std::ostream& out);

which is logic since its a member function I "normaly could use this to access the calling object"
the definition is as follows:

std::ostream& operator<<(std::ostream& out, point p)
{
    out<<p.abs << " " << p.ord <<endl;
}

now why in hell it didn't mentioned the deference between the number of arg between the declaration and teh definition and why it tells me I can't access my variables trough "this"

pulling my hears off :(

[Oralloy]

momotaro,

Do you know what a friend declaration does?

I'm saying that you do not need the declaration of operator<< in your class at all.

[momotaro]

in this case where should I declare it?
I looked everywhere and here is a link fro example:
http://www.java2s.com/Tutorial/Cpp/0...adinserter.htm

[Oralloy]

momotaro,

Your example has the << operator declared as friend inside the class phonebook, because it uses the private attributes of the class directly. In your case, your operator is using the public interface of MyPoint, so declaring it as friend is unnecessary.

How you declare the operator depends on how your project is structured....

You could have a separate header and c++ file for the operator. In which case, the header file simply declares as

#include <iostream>
#include <MyPoint.h>
 
std::ostream& operator<<(std::ostream& out, MyPoint &p);

You could simply in-line the entire operator in the header and dispense with the implementation file:

#include <iostream>
#include <MyPoint.h>
 
inline std::ostream& operator<<(std::ostream& out, MyPoint& p)
{
    out<<p.abs << " " << p.ord <<endl; 
}

Or, you can simply define the operator at the top of the single file that you use it in, and dispense with any abstract declaration.

It all really depends on how you are structuring your project, and what your goals are.

Cheers!