Does `new unsigned int` Initialize Memory to Zero in C ?

Operator new initializes memory to zero

In the following code snippet:

#include <iostream>

int main(){
  unsigned int* wsk2 = new unsigned int(5);
  std::cout <p>The expected result is that the memory is not initialized to zero, but the output is:</p>
<pre class="brush:php;toolbar:false">wsk2: 0x928e008 5
wsk2: 0x928e008 0

It seems that the operator new is initializing the memory to zero, but it is actually not.

How it works:

There are two versions of the operator new:

wsk = new unsigned int;      // default initialized (ie nothing happens)
wsk = new unsigned int();    // zero    initialized (ie set to 0)

The default initialization does not initialize the memory, while the zero initialization sets the memory to zero.

It also works for arrays:

wsa = new unsigned int[5];   // default initialized (ie nothing happens)
wsa = new unsigned int[5](); // zero    initialized (ie all elements set to 0)

To confirm that the memory is actually zeroed out, we can use placement new with a known piece of memory:

#include <new>
#include <iostream>


int main()
{
    unsigned int   wsa[5] = {1,2,3,4,5};

    // Use placement new (to use a know piece of memory).
    // In the way described above.
    // 
    unsigned int*    wsp = new (wsa) unsigned int[5]();

    std::cout <p>The output of this code is:</p>
<pre class="brush:php;toolbar:false">0
0
0
0
0

Which confirms that the memory is indeed zeroed out by the zero-initialization version of the operator new.

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