CODEWITHSUNDEEP
c++
michalt38
michalt38

Reputation: 1203

Zero initialization of non-POD

Why in the following non-POD class the x is initalized to zero?

class test {
public:
    void print() {
        cout << x << endl;
    }
private:
    int x;
};

int main(int argc, char** argv)
{
    test * tst = new test();
    tst->print();
    cout << is_pod<test>::value << endl;
}

Both tst->print() and is_pod() returns 0

Upvotes: 3

Views: 203

Answers (1)

Evg
Evg

Reputation: 26302

This is a result of value-initialization of a class without a user-provided constructor.

In this case, T() and new T() perform zero-initialization first:

if T is a class type with a default constructor that is neither user-provided nor deleted (that is, it may be a class with an implicitly-defined or defaulted default constructor), the object is zero-initialized and then it is default-initialized if it has a non-trivial default constructor;

The effects of zero-initialization are:

if T is an non-union class type, all base classes and non-static data members are zero-initialized, and all padding is initialized to zero bits. The constructors, if any, are ignored.

and

if T is a scalar type, the object's initial value is the integral constant zero explicitly converted to T.

Upvotes: 6

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