What is the actual concept of delete operator?

[MrError]

Hello all. I am c++ beginner. I am not getting the real concept of delete operator. If it deallocates the memory, then why i am getting such output..!!

int main()
{
    int *a , b=5;
    a = & b;
    cout << *a << endl;
    delete a;
    cout << *a;
    getch();
    return 0;   
}

Output:
5
5

[weaknessforcats]

The rule is: He who allocates is he who deletes.

When you allocate using the new operator, you receive a pointer to that object. The object will exist until you delete it.

The compiler never uses the delete operator since it always deletes when the object goes out of scope.

In the case above, when the pointer to the object allocated by new goes out of scope, the pointer is deleted but not the object it points at. That's because the compiler allocated the pointer but you allocated the object. Here you must explicitly call delete to tell the compiler to deallocate the object.

Your posted example won't execute. It will crash trying to delete an object the compiler allocated but you did not.

[MrError]

What do you mean by explicitly calling delete and no, it did not crash!

[weaknessforcats]

An explicit delete is when you code the word delete.

Implicit delete:

{
    int x;
}

Explicit delete:

{
   int * ptr = new int;
   delete ptr;
}

As far as crashing goes, you cannot delete a local variable. If your program did not crash, you may look into a better compiler. Visual Studio.NET 2008 has no compile errors but the program will crash when attempting to delete the local variable.

[MrError]

Got it.
Thanks a lot for your help.