pointers in c++

Every variable in C++ has an address which is a hexadecimal number (a hexadecimal number always starts with “0x”), we can see the address of any variable in C++ if we put an ampersand(&) symbol before it.

#include<bits/stdc++.h> // It is basically a header file that includes every standard library
using namespace std;
int main()
{
    int var = 10;
    cout<<"address is : "<<&var; // 0x61ff0c
    return 0;
}

Pointers in c++/c is a variable that points to another variable i.e. a pointer stores the address of another variable.

int* p; // pointer declared and points to garbage value

This type of pointer declaration is not a very good practice as having pointers pointing to garbage values can be dangerous. It is always a good practice to give the address to your pointer while declaring it or else you can point it to NULL (all capital letters).

int var = 10;
int* ptr1 = &var; // stores address to variable var. (ptr1 points to var)
int* ptr2 = NULL; // points to NULL

Dereferencing pointers in c++

Pointers in c++ provide an alternative way to reach the value of the pointed variable.

int var = 10;
int* p = &var;

Now, we can access the value of the variable var in 2 ways

1. We can directly use the variable var to access its value (10 here)
2. We can deference the pointer to access the value of the variable var. we can dereference the pointer by placing an asterisk(*) before the pointer.
example : *p
*p prints 10 as p (pointer) points to var (variable)

Double pointer in c++

A double pointer in c++ is a variable that points to the address of another pointer.

#include<bits/stdc++.h> // It is basically a header file that includes every standard library
using namespace std;
int main()
{
    int var = 10;
    int* ptr1 = &var;
    int** ptr2 = &ptr1;
    cout<<"var : "<<var<<"\n";
    cout<<"*ptr1 : "<<*ptr1<<"\n";
    cout<<"**ptr2 : "<<**ptr2<<"\n";
    return 0;
}

All the 3 cout statements print 10. a double pointer is declared like int** ptr2 = &ptr1; . The double-pointer needs 2 asterisks (**) and the triple pointer similarly needs 3 asterisks(***) and so on.

Remember a double-pointer can only store the address of a pointer and a triple pointer can only store the address of a double-pointer and so on.

To get a deep understanding of memory layout in C and C++ refer to this link.

Refer GeeksForGeeks for more information on pointers in c++.