I encountered some thing weird code in Dynamic memory allocation for 2D arrays in C++? please explain me what is this?

Question

code:- p = new int *[5];
where p is a pointer & declared as int **P;

Please explain me that why there is a * in between new and [5].

Answer 1

When allocating an array using new you need to specify the type. The general pattern is:

type* x = new type[n];

Where type is the base type, x is the variable, and n is the number of entries. You can make this a pointer type by adding * to both sides:

type** x = new type*[n];

You can continue this indefinitely:

type**** x = new type***[n];

Though in practice you'd rarely see that since excessively deep structures like that are nothing but trouble.

In C++, by virtue of its C heritage, pointers and arrays are interchangeable, as in both these definitions are basically equivalent:

void f(int* x)
void f(int x[])

Internally you can use x as either a pointer or an array, or both:

int y = x[0];
int z = *x;

Likewise these are identical:

int y = x[1];
int z = *(x + 1);

In general the distinction between x[n] and *(x + n) is largely irrelevant, the compiler treats both as the same and the emitted machine code is identical. The [] notation is just a syntax element that helps make the code easier to follow.