Programming Forums > Application Development > C++

-=PARADOX=- · Nov 10th, 2005, 11:08 AM

Hello to all...

I'm trying to redefine the output << and input >> operators, the prototype of the function in the class looks like this:

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ostream& operator<<( ostream &stream, const CString );

When I compile ( i'm using c++ builder 6 ) it gives this errors on the above function:

(Toggle Plain Text)

Type name expected
Declaration missing

What i'm doing wrong???

stevengs · Nov 10th, 2005, 11:25 AM

Quote:

Originally Posted by -=PARADOX=-

(Toggle Plain Text)

ostream& operator<<( ostream &stream, const CString );

...( ostream & stream, const CString what? )

Polyphemus_ · Nov 10th, 2005, 11:29 AM

Quote:

Originally Posted by stevengs

...( ostream & stream, const CString what? )

that doesn't matter, when defining you don't have to name the arguments passed to the function.

stevengs · Nov 10th, 2005, 11:29 AM

Quote:

Originally Posted by Polyphemus_

that doesn't matter, when defining you don't have to name the arguments passed to the function.

right... duh. But should it not be better a reference to a CString? Please provide the definition and an example call.

-=PARADOX=- · Nov 10th, 2005, 12:22 PM

Sorry i forget the &

...

Here is the definition:

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ostream& operator<<( ostream &stream, const CString &str1)
{
        stream << str;
        return stream;
}

Another question... should i implement the function inside the class or outside it using the friend keyword?

Animatronic · Nov 10th, 2005, 12:59 PM

I always do inside the class def from simplicity e.g

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class foo
{
	int a;
public:
	friend std::ostream& operator << ( std::ostream& os, foo const & f )
	{
		os << f.a;
		return os;
	}
};

btw isnt this:

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ostream& operator<<( ostream &stream, const CString &str)
{
        stream << str; <<<<<<<<
        return stream;
}

going to cause an inifinte loop...

-=PARADOX=- · Nov 10th, 2005, 1:13 PM

ups... i messed up things again... my code is:

(Toggle Plain Text)

ostream& operator<<( ostream &stream, const CString &str)
{
        stream << str.str; // str.str is a c style string
        return stream;
}

So I use the friend keyword, but where I declare that function?

By the way, c++ builder does't seem to like the ostream... for example:

(Toggle Plain Text)

#include <ostream>

int main()
{
        ostream stream;

        return 0;
}

It produces this error: "'Could not find match for 'ostream::basic_ostream()'"

Help...

Animatronic · Nov 10th, 2005, 1:23 PM

Thats because ostream is in the std namespace, so you either need using namespace std; after your includes, or specify the namespace (like I did before) with std:: infront of the class/object/etc.

You need the friend because the operator << ( std::ostream, CString cons ) is not a member function and so the private member variables can not be accessed without friend before the definition. If you only acces const member functions within the operator then the operator dosent need to be a friend.

-=PARADOX=- · Nov 10th, 2005, 1:27 PM

Even if i put 'using namespace std' it gives the same error.....

Animatronic · Nov 10th, 2005, 1:38 PM

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#include <iostream>

using namespace std;

class foo
{
	int a;
public:
	friend ostream& operator << ( ostream & os, foo const & f  )
	{
		os << f.a << std::endl;
		return os;
	}
};

int main()
{
	foo f;

	cout << f << endl;

	return 0;
}

That should work ^^ (it does for me).

What I said before about needed the friend because the operator wasnt a member function was wrong, its just the way I learnt it. There are some problems with the stream's not working with class operators only with global ones (because of the ordering of variables I think), maybe some one else with help clarify the stituation.

Nov 10th, 2005, 11:08 AM	#1
-=PARADOX=- Programmer Join Date: Oct 2005 Location: Portugal Posts: 53 Rep Power: 3	ostream Hello to all... I'm trying to redefine the output << and input >> operators, the prototype of the function in the class looks like this: (Toggle Plain Text) ostream& operator<<( ostream &stream, const CString ); ostream& operator<<( ostream &stream, const CString ); When I compile ( i'm using c++ builder 6 ) it gives this errors on the above function: (Toggle Plain Text) Type name expected Declaration missing Type name expected Declaration missing What i'm doing wrong???

Nov 10th, 2005, 12:22 PM	#5
-=PARADOX=- Programmer Join Date: Oct 2005 Location: Portugal Posts: 53 Rep Power: 3	Sorry i forget the & ... Here is the definition: (Toggle Plain Text) ostream& operator<<( ostream &stream, const CString &str1) { stream << str; return stream; } ostream& operator<<( ostream &stream, const CString &str1) { stream << str; return stream; } Another question... should i implement the function inside the class or outside it using the friend keyword?

Nov 10th, 2005, 12:59 PM	#6
Animatronic Programmer Join Date: Jun 2005 Posts: 99 Rep Power: 4	I always do inside the class def from simplicity e.g (Toggle Plain Text) class foo { int a; public: friend std::ostream& operator << ( std::ostream& os, foo const & f ) { os << f.a; return os; } }; class foo { int a; public: friend std::ostream& operator << ( std::ostream& os, foo const & f ) { os << f.a; return os; } }; btw isnt this: (Toggle Plain Text) ostream& operator<<( ostream &stream, const CString &str) { stream << str; <<<<<<<< return stream; } ostream& operator<<( ostream &stream, const CString &str) { stream << str; <<<<<<<< return stream; } going to cause an inifinte loop...

Nov 10th, 2005, 1:13 PM	#7
-=PARADOX=- Programmer Join Date: Oct 2005 Location: Portugal Posts: 53 Rep Power: 3	ups... i messed up things again... my code is: (Toggle Plain Text) ostream& operator<<( ostream &stream, const CString &str) { stream << str.str; // str.str is a c style string return stream; } ostream& operator<<( ostream &stream, const CString &str) { stream << str.str; // str.str is a c style string return stream; } So I use the friend keyword, but where I declare that function? By the way, c++ builder does't seem to like the ostream... for example: (Toggle Plain Text) #include <ostream> int main() { ostream stream; return 0; } #include <ostream> int main() { ostream stream; return 0; } It produces this error: "'Could not find match for 'ostream::basic_ostream()'" Help...

Nov 10th, 2005, 1:38 PM	#10
Animatronic Programmer Join Date: Jun 2005 Posts: 99 Rep Power: 4	(Toggle Plain Text) #include <iostream> using namespace std; class foo { int a; public: friend ostream& operator << ( ostream & os, foo const & f ) { os << f.a << std::endl; return os; } }; int main() { foo f; cout << f << endl; return 0; } #include <iostream> using namespace std; class foo { int a; public: friend ostream& operator << ( ostream & os, foo const & f ) { os << f.a << std::endl; return os; } }; int main() { foo f; cout << f << endl; return 0; } That should work ^^ (it does for me). What I said before about needed the friend because the operator wasnt a member function was wrong, its just the way I learnt it. There are some problems with the stream's not working with class operators only with global ones (because of the ordering of variables I think), maybe some one else with help clarify the stituation.

Nov 10th, 2005, 1:23 PM	#8
Animatronic Programmer Join Date: Jun 2005 Posts: 99 Rep Power: 4	Thats because ostream is in the std namespace, so you either need using namespace std; after your includes, or specify the namespace (like I did before) with std:: infront of the class/object/etc. You need the friend because the operator << ( std::ostream, CString cons ) is not a member function and so the private member variables can not be accessed without friend before the definition. If you only acces const member functions within the operator then the operator dosent need to be a friend.

Nov 10th, 2005, 1:27 PM	#9
-=PARADOX=- Programmer Join Date: Oct 2005 Location: Portugal Posts: 53 Rep Power: 3	Even if i put 'using namespace std' it gives the same error.....

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