About whether the new C + + is going to initialize the memory problem __c++

Original address: Http://hi.baidu.com/maxy218/item/8cd098256327c1829d63d1ca

Put the conclusion first:

C + + initialization in new may be as follows: For classes with constructors, regardless of parentheses, constructors are initialized; if there is no constructor, then new without parentheses allocates only memory space and does not initialize memory. New with parentheses is initialized to 0 while allocating memory.

The following code:

#include <iostream>

using namespace Std;

int main ()
{
int *a=new int[1000];
for (int i=0;i<1000;i++) {
a[i]=i+1;
}
Delete[] A;
int *b=new int[1000];
for (int i=0;i<100;i++) {
cout<<b[i]<<endl;
}

return 0;
}

Not initialized, the result of the output is:

9437380

9443448

3

4

5

6

。。。

Visible, the new operator does not initialize memory.

and slightly change the code (add parentheses after new ()):

#include <iostream>

using namespace Std;

int main ()
{
int *a=new int[1000];
for (int i=0;i<1000;i++) {
a[i]=i+1;
}
Delete[] A;
int *b=new int[1000] ();
for (int i=0;i<100;i++) {
cout<<b[i]<<endl;
}

return 0;
}

The output results are:

0

0

0

0

。。

Visible, has been initialized.

=============================================================================

Further thinking:

Define Class A:

Class a{
Public
int A;
A (): A (10) {};
};

Use the statement in the main function:

A *b=new A;
cout<<b->a<<endl;

A *b=new a ();
cout<<b->a<<endl;

The output is 10, and all of the results are initialized.

However, if the constructor of bar A is deleted, the output of the two statements is: random number, 0.

Thus, C + + in new initialization of the law may be: For a class with constructors, regardless of parentheses, are initialized with constructors; if there is no constructor, the new without parenthesis allocates only the memory space, and does not initialize the memory. New with parentheses is initialized to 0 while allocating memory.