Constructor to specify zero-initialization of all builtin members?

Question

Is there a simpler way for a class's constructor to specify that all members of built-in type should be zero-initialized?

This code snippet came up in another post:

struct Money
{
    double amountP, amountG, totalChange;
    int twenty, ten, five, one, change;
    int quarter, dime, nickel, penny;

    void foo();
    Money()  {}
};

and it turned out that the problem was that the object was instantiated via Money mc; and the variables were uninitialized.

The recommended solution was to add the following constructor:

Money::Money()
  : amountP(), amountG(), totalChange(),
    twenty(), ten(), five(), one(), change()
    quarter(), dime(), nickel(), penny()
{
}

However, this is ugly and not maintenance-friendly. It would be easy to add another member variable and forget to add it to the long list in the constructor, perhaps causing a hard-to-find bug months down the track when the uninitialized variable suddenly stops getting 0 by chance.

Answer 1

You can use a subobject to initialize en masse. A member works, but then you need to qualify all access. So inheritance is better:

struct MoneyData
{
    double amountP, amountG, totalChange;
    int twenty, ten, five, one, change;
    int quarter, dime, nickel, penny;
};

struct Money : MoneyData
{
    void foo();
    Money() : MoneyData() {} /* value initialize the base subobject */
};

Demonstration (placement new is used to make sure the memory is non-zero before object creation): http://ideone.com/P1nxN6

Contrast with a slight variation on the code in the question: http://ideone.com/n4lOdj

In both of the above demos, double members are removed to avoid possible invalid/NaN encodings.