CODEWITHSUNDEEP
c++overloadingoperator-keyword
Piotr Suchanek
Piotr Suchanek

Reputation: 384

Operator overloading in C++ "<<"

I try to overload operator in C++, but I am having some difficulties. This is what I have in my class:

ostream & operator <<(ostream & s)
 {
  s << w();
 return s;

}
 string w()
{
stringstream ss;
string str;
for (int i=n-1; i>=0; i--)
{
    if (i==n-1)
    {
        ss<<tablica[i] << "x^" << i;
    }
    else
    {
        if (tablica[i]<eps && tablica[i]>-eps) ss <<"+" << +tablica[i]<< "x^" << i;
        else if (tablica[i]<eps)ss << tablica[i]<< "x^" << i;
        if(tablica[i]>eps) ss <<"+" << +tablica[i]<< "x^" << i;
    }

}
ss >> str;
return str;

}

I am trying to use this like this:

cout << p << endl;

Error: no match for 'operator<<' in 'std::cout << p Here is my whole code of program: http://codepad.org/xBijPMCp

Upvotes: 0

Views: 1527

Answers (4)

Tarun Mehmi
Tarun Mehmi

Reputation: 11

Operator overloading is the ability to tell the compiler how to perform a certain operation when its corresponding operator is used on one or more variables.

For example, the compiler acts differently with regards to the subtraction operator - depending on how the operator is being used.

  • When it is placed on the left of a numeric value such as -48, the compiler considers the number a negative value.
  • When used between two integral values, such as 80-712, the compiler applies the subtraction operation.
  • When used between an integer and a double-precision number, such as 558-9.27, the compiler subtracts the left number from the right number; the operation produces a double-precision number.
  • When the - symbol is doubled up and placed on one side of a variable, such as --Variable or Variable--, the value of the variable needs to be decremented; in other words, the value 1 shall be subtracted from it.

All of these operations work because the subtraction operator - has been reconfigured in various classes to act appropriately.

Upvotes: 1

qPCR4vir
qPCR4vir

Reputation: 3571

You first need to think about your general design. I think you want to overload << to work with the type of your variable tablica. The operator<<() is a binary operator: the declaration have to be of the form: <<(Type t1, Type t2). (is you want it to be a member this will "degenarte" to only one parametr, because the first-the left, will be a kind of this). In your case something like:

ostream & operator <<(ostream & s, const tablica_type &c);

Your tablica is a global variable, and n too, with normaly is not a good idea. You will probably want to define a class woth hold the tablica and the n, and for this class override <<().

Upvotes: 0

Jerry Coffin
Jerry Coffin

Reputation: 490048

An overloaded operator is invoked in one of two ways. Either as a member function, where x op y; is treated as x.op(y); or else a global, where x op y; becomes op(x,y);.

Note that when the operator is a member function, the left operand must be the one for which you overload the operator. In the case of inserting into a stream: x << y;, the left operand is the stream object, so to overload the operator as a member function, you'd have to do the overload as a member of the stream class.

Since modifying the stream classes is pretty much off-limits, your only real choice is to implement the overload as a global function. In this case, however, the function must take two parameters (one for the left operand, one for the right operand).

Therefore, an insertion operator nearly always needs a signature like:

std::ostream &operator<<(std::ostream &os, T const &t)

(where T is whatever type you're going to insert).

Upvotes: 2

spin_eight
spin_eight

Reputation: 4025

ostream & operator <<(ostream & s) should be implemented in the relation to a particular class(to make it usefull), so signature should be

friend ostream & operator <<(ostream & s, const class_name &c);

Upvotes: 4

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