Default initialization of C++ Member arrays?

Question

This is a simple question, but I can\'t seem to find a definitive answer.

If we have the following class:

class Test
{
...
  char testArray[10];

...         


        

Answer 1

It depends on may factors that you forgot to mention.

If your Test has no user-defined constructor or your user-defined constructor makes no efforts to initialize the array, and you declare the object of type Test as

Test test; // no initializer supplied

then it will behave in exactly the same way as you described above. For an automatic (local) object the contents of the array will remain unpredictable. For a static object the contents is guaranteed to be zero.

If your class has a user-defined constructor, then it will all depend on what constructor does. Again, keep in mind that static objects are always zero-initialized before any constructor has a chance to do anything.

If your class is an aggregate, then the content might depend on the aggregate initializer you supplied in the object declaration. For example

Test test = {};

will zero-initialize the array even for an automatic (local) object.