Constructor called with creating object

Question

class P{
    public:
    P(int x,int y) { cout << "constructor called" << endl;}
};

int main ()
{
    P(5,4);    // constructor called  
    P p(5,4);  // constructor called
    return 0;
}

What is the difference between the above two constructor calls?

How does P(5,4) call the constructor?

What are your doubts why the constructor shouldn't be called? The constructor function is called the same way for both examples. — πάντα ῥεῖ, Mar 03 '19 at 20:20

score 3 · Answer 1 · answered Mar 03 '19 at 20:20

3

Those two invocations are identical.

The only difference is in the second you hold the created object in a local variable p

answered Mar 03 '19 at 20:20

tinkertime

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score 0 · Answer 2 · answered Mar 04 '19 at 00:14

In C++ a type name followed by a (possibly empty) parenthesized list is a prvalue expression that (usually) results in creation of a temporary object of that type, and the list consists of the arguments to the constructor.

An exception to this is when there is syntactic ambiguity, see here.

Compare with P p = P(5,4); In P(5,4); you still have the same righthand side, but you just let the object be created and destroyed instead of associating it with a name p.

Constructor called with creating object

2 Answers2