Question

I want to declare and initialize a pointer, with a value (like 1000) and I don’t wanna use second variable. Please see below :

int *p = &1000;
Output: error : & on Constant

int *p = (int *)1000;
Output: 0000003E8

int *p = new int(1000);
Output: 1000

Since, first two methods are not giving the expected output. So, I would like to know, which one would be the correct method and why ?

Reference

Answer 1

According to your comment,

when i try to *p then, it display 1000. Now, whatever you got.

you would like to initialize the pointer such that it points to a place that stores the integer 1000. You do not want to initialize the pointer such that it points to the absolute address 1000.

Of the three lines of code you offered, only the last one does what you want:

int *p = new int(1000);

This allocates space for an int on the heap and value-initializes that space with 1000.

Notes:

• Allocating space for a single int on the heap may sometimes be necessary, but most of the time it won’t be useful, because an int is a very small object. The pointer may very well be just as large or larger, therefore passing around a pointer to an int, rather than passing around the int itself, is of limited use.

• If you really think you need this, keep in mind that you’ll need to deallocate that space later, using

  delete p;
  

• On a general note, most of the time you need to allocate space on the heap and maintain pointers to it, you are far better off using smart pointers (such as std::unique_ptr<int> or std::shared_ptr<int> in C++11) to avoid having to think of deallocation.