Pointer in C++

Pointer Variable Declarations and Initialization

Pointer variables contain memory address as their values.

Diagrams typically represent a pointer as an arrow from the variable that contains an address to the variable located at that address in memory.

int *countPtr;

Pointer should be initialized to 0, NULL or an address of the corresponding type either when they're declared or in an assignment.

A pointer with the value 0 or NULL "points to nothing" and is known as a null pointer.

Pointer Operators

The address operator(&) is a unary operator that obtains the address memory address of its operand.

int y = 5;  // declare variable y
int *yPtr;  // declare pointer variable yPtr
yPtr = &y;  // assign address of y to yPtr

Now, yPtr indirectly references variable y's value.

The * operator, commonly referred to as the indirection operator or dereferencing operator.

indirection operator

int y = 1;
int *yPtr = &y;

the value of yPtr is address of variable y.

dereferencing operator

*yPtr = 9;

would assign 9 th variable y.

Pointer and Array

Assume the following declarations:

int b[5];  // create 5-element int array b
int *bPtr; // create int pointer bPtr

Because the array name is a pointer to the first element of the array, we can set bPtr to the address of the first element in array b with the statement

bPtr = b;  // assign address of the array b to bPtr

also

bPtr = &b[0];  // also assigns address of array b to bPtr

Example

#include <iostream>
using namespace std;

int main()
{
  	int b[] = {10, 20, 30, 40};  // create 4-element array b
  	int *bPtr = b;  // set bPtr to point to array b
  
  	// output array b using array subscript notation
  	cout << "Array b printed with:

Array subscript notation
";
  	for (int i = 0; i < 4; i++)
    {
      	cout << "b[" << i << "] = " << b[i] << "
";
    }
  
  	// out array b using the array name and pointer/offset notation
  	cout << "
Pointer/offset notation where "
      	<< "the pointer is the array name
";
  	for (int offset1 = 0; offset1 < 4; offset1++)
    {
      	cout << "*(b + " << offset1 << ") = " << *(b + offset1) << "
";
    }
  
  	// output array b using bPtr and array subscript notation
  	cout << "
Pointer subscript notation
";
  	for (int j = 0; j < 4; j++)
    {
      	cout << "bPtr[" << j << "] = " << bPtr[j] << "
";
    }
  
  	cout << "
Pointer/offset notation
";
  
  	// out array b using bPtr and pointer/offset notation
  	for (int offset2 = 0; offset2 < 4; offset2++)
    {
      	cout << "*(bPtr + " << offset2 << ") = "
          	<< *(bPtr + offset2) << "
";
    }
}

output:

Array b printed with:

Array subscript notation
b[0] = 10
b[1] = 20
b[2] = 30
b[3] = 40

Pointer/offset notation where the pointer is the array name
*(b + 0) = 10
*(b + 1) = 20
*(b + 2) = 30
*(b + 3) = 40

Pointer subscript notation
bPtr[0] = 10
bPtr[1] = 20
bPtr[2] = 30
bPtr[3] = 40

Pointer/offset notation
*(bPtr + 0) = 10
*(bPtr + 1) = 20
*(bPtr + 2) = 30
*(bPtr + 3) = 40
Program ended with exit code: 0