Re: dynamic allocation and values of data members

From:
pjb@informatimago.com (Pascal J. Bourguignon)
Newsgroups:
comp.lang.c++
Date:
Mon, 14 Apr 2008 16:58:03 +0200
Message-ID:
<7ciqyk1o1w.fsf@pbourguignon.anevia.com>
"subramanian100in@yahoo.com, India" <subramanian100in@yahoo.com> writes:

Consider the following classes without ctors.

class Sample
{
private:
double d_val;
double* d_ptr;
};

class Test
{
private:
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
garbage."

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.

--
__Pascal Bourguignon__

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