C++ Pointers

Learning pointers in C++ is both simple and fun. Pointers can simplify the execution of some C++ programming tasks and enable others, such as dynamic memory allocation, which cannot be performed without them. Therefore, to become an excellent C++ programmer, learning pointers is essential.

As you know, every variable has a memory location, and each memory location defines an address that can be accessed using the ampersand (&) operator, representing an address in memory. Consider the following example, which outputs the addresses of defined variables:

Example

#include <iostream>

using namespace std;

int main ()
{
   int  var1;
   char var2[10];

   cout << "Address of var1 variable: ";
   cout << &var1 << endl;

   cout << "Address of var2 variable: ";
   cout << &var2 << endl;

   return 0;
}

When the above code is compiled and executed, it produces the following result:

Address of var1 variable: 0xbfebd5c0
Address of var2 variable: 0xbfebd5b6

Through the above example, we understand what a memory address is and how to access it. Next, let's see what a pointer is.

What is a Pointer?

A pointer is a variable whose value is the address of another variable, i.e., the direct address of a memory location. Like other variables or constants, you must declare a pointer before using it to store the address of another variable. The general form of a pointer variable declaration is:

type *var-name;

Here, type is the base type of the pointer, which must be a valid C++ data type, and var-name is the name of the pointer variable. The asterisk * used to declare a pointer is the same asterisk used for multiplication. However, in this statement, the asterisk is used to designate that the variable is a pointer. The following are valid pointer declarations:

int    *ip;    /* Pointer to an integer */
double *dp;    /* Pointer to a double */
float  *fp;    /* Pointer to a float */
char   *ch;    /* Pointer to a character */

The actual data type of the value of all pointers, whether integer, float, character, or otherwise, is the same, a long hexadecimal number that represents a memory address. The only difference between pointers of different data types is the data type of the variable or constant that the pointer points to.

Using Pointers in C++

Several operations are commonly performed with pointers: defining a pointer variable, assigning the address of a variable to a pointer, and accessing the value at the address available in the pointer variable. These operations are performed using the unary operator * which returns the value of the variable located at the address specified by its operand. The following example involves these operations:

Example

#include <iostream>

using namespace std;

int main ()
{
   int  var = 20;   // Declaration of the actual variable
   int  *ip;        // Declaration of the pointer variable

   ip = &var;       // Store the address of var in the pointer variable

   cout << "Value of var variable: ";
   cout << var << endl;

   // Output the address stored in the pointer variable
   cout << "Address stored in ip variable: ";
   cout << ip << endl;

   // Access the value at the address in the pointer
   cout << "Value of *ip variable: ";
   cout << *ip << endl;

   return 0;
}

When the above code is compiled and executed, it produces the following result:

Value of var variable: 20
Address stored in ip variable: 0xbfc601ac
Value of *ip variable: 20

Detailed Explanation of C++ Pointers

In C++, there are several concepts related to pointers that are simple yet important. Below are some key concepts that C++ programmers must be aware of: