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Why doesn't this work? (pointers)

I wrote the following program to demonstrate an oddity I found in C++.

#include <iostream>
using namespace std;
int main()
{int *p, *q;
p = q;
q = new int;
*q = 12;
cout << *p;
system("pause") ;
return 0;
Your compiler will either give a gibberish answer or crash when you try
to run this program.
Here's what I don't understand: p and q are pointing to the same memory
address. That being said, why can't you access the dynamic variable using
p as well as q?
What would happen if you created a new variable using p too? Aren't they
both pointing to the same memory? Would they overwrite each other?


I actually came across this while working with a homemade linked list.
You can imagine how frustrating THAT was...
Jul 22 '05
22 1512
Mike Wahler wrote:
The difference between our assertions is that you qualified
with 'POD' (and I used 'automatic' instead of 'default').
Yes, without the qualification of POD types, your statement
is wrong. The defect in the language is that automatic POD
types are not default initalized when other non-POD types
would be.

I think you're confusing me. What about such an object
initialized via an argument? (OR do you mean only those
declarations lacking an initializer?)

Default initialization, i.e., those without explicit initializers.
Jul 22 '05 #21
I was actually asking a genuine question, although I was pretty sure of
the answer. I get burned every now and then with "things in C++ what is
different than C". I didn't think there was a prohibition, and as I
recall some compilers do that in debug mode.

Right, there is no prohibition. The compiler is just not required
to initialize POD types in certain circumstances.

This whole initialization debacle, and the bandaids the standards
committee put on it with value initailziation is just odiferous slavish
following of the way things were always done in C. It causes more
problems than it solves, and if it were changed today, it would break
no code (although some people who rely on not using RAII might get a
little slower). If you want to skip default initialization, I think
that should be the explicit case.
Jul 22 '05 #22
Ron Natalie wrote:
Yes, without the qualification of POD types, your statement
is wrong. The defect in the language is that automatic POD
types are not default initalized when other non-POD types
would be.

Actually it is not a defect.
Check this message:


Ioannis Vranos

Jul 22 '05 #23

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