Re: dynamic allocation and values of data members

"Victor Bazarov" <>
Mon, 14 Apr 2008 11:09:09 -0400
Pascal J. Bourguignon wrote:

", India" <>

Consider the following classes without ctors.

class Sample
double d_val;
double* d_ptr;

class Test
int i_val;
int* i_ptr;
Sample obj;

Suppose I allocate
Test* t = new Test();

Since I have mentioned 'new Test()' instead of just 'new Test',
will this statement set
t->i_val to zero, t->i_ptr to null pointer, t->obj.d_val to 0.0,
t->obj.d_ptr to null pointer ?

What does the standard say in this regard ?

I just asked this question to my local C++ guru this morning, and he
said that no, these members are not implicitely initialized. You have
to do it yourself. The problem is that "[p]rimitive type member
variable like int, float etc does not have any constructors, so they
are just initialized with an undefined initial value which is often a

Your guru needs to refresh his knowledge of the initialisation process.
Tell him to look things up in the Standard.

Note that you should probably always define a constructor (perhaps
private), to let other objects use your class for its member and have
it automatically initialized with default values.

The expression

    Test* t = new Test();

in OP's case _value-initialises_ the object. That means, since 'Test'
is *not* a POD, it would call the default constructor for the class if
one existed, but since there is no user-defined constructor, every
member is _value-initialised_. For a POD type it measn _zero_-
initialised. Same proceeds to 'Sample'.

IOW, all arithmetic values are 0 and all pointers are null.

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