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C++: << Operator does not work as expected

Posted on 2010-11-16
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Last Modified: 2012-05-10
I am trying to overload the << operator.

I have a custom class called person.

I added this to person.h:

public:
.....
....
ostream &person::operator<<(ostream &stream);

I added this to person.cpp
....
....
ostream &person::operator<<(ostream &stream) {
            stream << this->getAge()  << " ";
            return stream;
      }

In the main function, I did the following.
person P4 = person("C", "C", 23); //first name, last name and age
cout << &P4 << " ";

The code compiles fine but when I run the code, I see this output:
0012FDFC

I am expecting output:
23

I am using Visual Studio 2008.

Not sure what am I doing wrong. Please help. Thanks in advance.
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Question by:shekhar_shashi
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7 Comments
 
LVL 44

Assisted Solution

by:AndyAinscow
AndyAinscow earned 400 total points
ID: 34149200
&P4 means the memory adress of P4

does this do what you expect
cout << P4 << " ";
0
 
LVL 3

Author Comment

by:shekhar_shashi
ID: 34149276
If I change the code this way, I get this compilation error:

error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'person' (or there is no acceptable conversion)      
0
 
LVL 86

Accepted Solution

by:
jkr earned 1600 total points
ID: 34149422
That's what evilrix' point was in your last question - you better make that
class person; // foward declaration

ostream& operator<< ( ostream& os, const student& p) ;

class person
{
  friend ostream& operator<< ( ostream& os, const person& p) ;

  // ...

};

ostream& operator<< ( ostream& os, const person& p)
{
  os << p.getAge();

  return 0s;
}

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LVL 3

Author Comment

by:shekhar_shashi
ID: 34149717
Pardon my C++ ignorance here.

I am getting about 9 compilation errors after making these code changes.

Instead of posting all the compilation errors, let me ask a few questions:

Question 1:
Where should the forward declaration go?

class person; // foward declaration

ostream& operator<< ( ostream& os, const student& p) ;

Question 2: I am guessing this code needs to be placed in the header file.

class person
{
  friend ostream& operator<< ( ostream& os, const person& p) ;

  // ...

};

Am I correct?

Question 3:

I am guessing this code will be placed in the person.cpp file.

ostream& operator<< ( ostream& os, const person& p)
{
  os << p.getAge();

  return 0s;
}
 
Am I correct?

Thanks.


0
 
LVL 86

Assisted Solution

by:jkr
jkr earned 1600 total points
ID: 34149837
1. Just above the operator's declaration

2. Actually, you just need to add
  friend ostream& operator<< ( ostream& os, const person& p) ;

to the declaration of the 'person' class.

3. You're absolutely correct ;o)
0
 
LVL 3

Author Comment

by:shekhar_shashi
ID: 34149879
Your answer was spot on.  Thanks a bunch for helping out this C++ newbie.
0
 
LVL 3

Author Closing Comment

by:shekhar_shashi
ID: 34149904
Thanks
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