Solved

How to overload << operator for a class?

Posted on 2007-03-23
9
246 Views
Last Modified: 2010-04-01
Hi,

How do we overload the stream operator for a class again? I want to do this:

class Something {
    int a;
    double d;
    void OverloadedStreamOperator <<()
    {
        ????
    }
};

int main()
{
    Something s;
    s.a = 44;
    s.d = 34.34;
    cout << s << endl;
}

Thanks
0
Comment
Question by:DJ_AM_Juicebox
  • 4
  • 3
  • 2
9 Comments
 
LVL 53

Expert Comment

by:Infinity08
ID: 18782467
 ostream& operator<< (ostream& os, const Something& s)
  {
    return os << s.a << " " << s.d << endl;
  }
0
 

Author Comment

by:DJ_AM_Juicebox
ID: 18782538
I tried adding that as a member of my class but get this compiler error:

     binary 'operator <<' has too many parameters
0
 
LVL 86

Expert Comment

by:jkr
ID: 18782537
Note that this is not a member operator, but an operator at global scope, so to make that work you'll usually have to make it a 'friend' of your class to use for non-public members also, i.e.

 ostream& operator<< (ostream& os, const Something& s)
  {
    return os << s.a << " " << s.d << endl;
  }
class Something {

friend ostream& operator<< (ostream&, const Something&);

    int a;
    double d;

};
0
Courses: Start Training Online With Pros, Today

Brush up on the basics or master the advanced techniques required to earn essential industry certifications, with Courses. Enroll in a course and start learning today. Training topics range from Android App Dev to the Xen Virtualization Platform.

 

Author Comment

by:DJ_AM_Juicebox
ID: 18782552
is there any way to make it a member of the class? Otherwise I'll have all these friends for all my classes at global scope?
0
 
LVL 53

Expert Comment

by:Infinity08
ID: 18782563
Or completely with your class :

class Something {
    int a;
    double d;
  public :
    friend istream& operator>>(istream& is, Something& s);
    friend ostream& operator<<(ostream& os, const Something& s);
};

istream& operator>>(istream& is, Something& s) {
  is >> s.a;
  is >> s.d;
  return is;
}
ostream& operator<<(ostream& os, const Something& s) {
  os << "a = " << s.a << endl;
  os << "d = " << s.d << endl;
  return os;
}
0
 
LVL 86

Expert Comment

by:jkr
ID: 18782586
>>is there any way to make it a member of the class?

No, the '<<' operator has a 'left to right' association. You can make a

Something s;

s << "whatever";

a member, but not a

ostream os;

os << s;
0
 
LVL 86

Accepted Solution

by:
jkr earned 500 total points
ID: 18782660
BTW, you could also add a 'write()' method like

class Something {
    int a;
    double d;
    ostream& write(ostream& os) const
    {
        os << a;
        os << d;

        return os;
    }
};

0
 

Author Comment

by:DJ_AM_Juicebox
ID: 18782690
yeah i ended up just doing a write() function. How sad!

Thanks
0
 
LVL 86

Expert Comment

by:jkr
ID: 18782711
I'd actually have chosen the 'friend' approach. It is just a C++ concept that your friends have access to your privates (pardon the pun ;o)
0

Featured Post

Courses: Start Training Online With Pros, Today

Brush up on the basics or master the advanced techniques required to earn essential industry certifications, with Courses. Enroll in a course and start learning today. Training topics range from Android App Dev to the Xen Virtualization Platform.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
What does std::atomic give me? 7 124
how to understand recursion 12 226
Embarcadero WebBroker REST server endpoint parameters 2 67
Installshield for Embarcadero EX 10.1 Berlin 4 40
Often, when implementing a feature, you won't know how certain events should be handled at the point where they occur and you'd rather defer to the user of your function or class. For example, a XML parser will extract a tag from the source code, wh…
Many modern programming languages support the concept of a property -- a class member that combines characteristics of both a data member and a method.  These are sometimes called "smart fields" because you can add logic that is applied automaticall…
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.

776 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question