CODEWITHSUNDEEP
c++parameters
studentlyfe
studentlyfe

Reputation: 21

What exactly is happening when we have unnamed parameters in these functions?

I was looking at an iterator class for a linked list and saw this operator overloading and didn't really understand what was going on. I was under the impression that 'int' always has to be declared with a variable name?

   void operator++(int)
    {
            assert(m_node != NULL);
            m_node = m_node->m_next;
    }

    void operator--(int)
    {
            assert(m_node != NULL);
            m_node = m_node->m_prev;
    }

Upvotes: 2

Views: 71

Answers (4)

MateuszZawadzki
MateuszZawadzki

Reputation: 149

Because you have two ++ operators, it is a special syntax to differentiate them between post- and pre- incrementation.

void operator++(int)

means postincrementation

void operator++()

means preincrementation

So in your case, you first return, then increase.

Upvotes: 2

Mike Seymour
Mike Seymour

Reputation: 254451

You can always leave out a parameter name if you want to. If you do that in a normal function definition, that means that an argument must still be provided to the function, but the function doesn't use it:

void f(int) // unnamed parameter
{
    // can't use the parameter without a name
}

f();   // ERROR: wants an int
f(42); // OK: takes an int (but ignores it)

In the case of the increment and decrement operators, an unused int parameter is the magic that indicates that this is the postfix operator, x++, not the prefix operator, ++x, which has no parameters.

Upvotes: 4

ravi
ravi

Reputation: 10733

void operator++(int)

This means post increment operator. int is just a dummy variable to distinguish it from pre-increment operator. Compiler would pass 0 in its place when calling post increment operator.

Upvotes: 1

David G
David G

Reputation: 96810

Parameter names are always optional. However, the int in this case is special as it denotes this is a postfix operator meaning you are able to do list++ and list--.

Reference: http://en.cppreference.com/w/cpp/language/operators

Upvotes: 4

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