Value of pointers at declaration C++

Question

When I declare something like

int *i = new int;

what is the value it is initialized to (by the compiler). If I want to make sure it is zero would I have to use

int *i = new int(0);

will new initialize everything to zero?

on the same topic what will be initialized by the compiler what will have to be user (when it comes to pointers).

`int* i = new int();` would zero-initialize the dynamically allocated `int`. — juanchopanza, Jul 07 '14 at 19:24
**1st of all**: why would you want to do this in favor over `int i = 0;`? — πάντα ῥεῖ, Jul 07 '14 at 19:24
`int *i = new int;` does **not** initialize the object pointed to by `i`. — The Paramagnetic Croissant, Jul 07 '14 at 19:25
@user3477950 _'does not initialize the object pointed to by i'_ Eeeh, what please?!? — πάντα ῥεῖ, Jul 07 '14 at 19:26
@πάνταῥεῖ I wouldn't assume that OP *prefers* `int *i = new int` over `int i`. It is quite clear that he is interested in the semantics of the initialization of dynamically allocated objects. — The Paramagnetic Croissant, Jul 07 '14 at 19:28
@πάνταῥεῖ Well, it initializes it but the initialization performs no initialization! — juanchopanza, Jul 07 '14 at 19:28
See also http://stackoverflow.com/questions/7546620/operator-new-initializes-memory-to-zero — Xavier Leclercq, Jul 07 '14 at 19:28
@πάνταῥεῖ Read what I mean: `int *i = new int;` does not zero-initialize `*i`. It leaves the storage uninitialized. It does not *construct,* it only *allocates.* — The Paramagnetic Croissant, Jul 07 '14 at 19:28
@πάνταῥεῖ `int` has no constructor. It's not a class type. — The Paramagnetic Croissant, Jul 07 '14 at 19:31
@πάνταῥεῖ The `int` does not get zero-initialized, that is the point. You need `int* i = new int();` for that, as I said in my first comment. — juanchopanza, Jul 07 '14 at 19:31

Vlad from Moscow · Accepted Answer · 2014-07-07T19:56:55.403

2

These two declarations

int *i = new int;

int *i = new int(0);

are equivalent in the sense that the both allocate memory dynamically (in the heap). So the both pointers will be initialized. However the memory itself in the first case is not initialized and has some arbitrary value while in the second case the memory (that is the object of type int that was allocated) is initialized by 0.

edited Jul 07 '14 at 19:56

answered Jul 07 '14 at 19:34

Vlad from Moscow

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Prefer "allocate memory dynamically" to "allocate on the heap". It's an uncertain and entirely irrelevant implementation detail whether the allocation happens "on the heap" or "on the stack" or anything else. What's important is the abstract semantics and the consequential behavior and/or correctness of the program. – The Paramagnetic Croissant Jul 07 '14 at 19:39

Value of pointers at declaration C++

1 Answers1