Pointers in c++

Pointers in c++

Pointers in c++ programming language are easy to learn. Some C++ tasks are performed more easily with pointers, and other C++ tasks like dynamic memory allocation, cannot be performed without them.

Every variable is a memory location and every memory location has its address defined which can be accessed using ampersand (&) operator which denotes an address in memory. By consider the following program which will print the address of the variables as defined:

#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;
}

The result produced for the given program will be :

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

What Are Pointers?

A pointer is a variable whose value is the address of another variable. Like any variable or constant, we must declare a pointer before we can work with it. The general form of a pointer variable declaration is:

type *var-name;

Here, type is the pointer’s base type; it must be a valid C++ type and var-name is the name of the pointer variable. The asterisk you used to declare a pointer is the same asterisk that you use for multiplication. However, in this statement the asterisk is being used to designate a variable as a pointer. Following are the valid pointer declaration:

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

The actual data type of the value of all pointers, whether integer, float, character, or any other, is 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++:

There are few important operations, which we will do with the pointers very frequently.

1.we define a pointer variables

2.assign the address of a variable to a pointer and

3.finally access the value at the address available in the pointer variable.

This is done by using unary operator * that returns the value of the variable located at the address specified by its operand. Following example makes use of these operations:

#include <iostream>

using namespace std;

int main ()
{
   int  var = 20;   // actual variable declaration.
   int  *ip;        // pointer variable 

   ip = &var;       // store address of var in pointer variable

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

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

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

   return 0;
}

When the above program is executed, it produces result as given below:

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

C++ Pointers in Detail:

Pointers have many things but they are easy concepts and they are very important to C++ programming language.

Concept	Description
C++ Null Pointers	C++ supports null pointer, which is a constant with a value of zero defined in several standard libraries.
C++ pointer arithmetic	There are four arithmetic operators that can be used on pointers: ++, –, +, –
C++ pointers vs arrays	There is a close relationship between pointers and arrays. Let us check how?
C++ array of pointers	You can define arrays to hold a number of pointers.
C++ pointer to pointer	C++ allows you to have pointer on a pointer and so on.
Passing pointers to functions	Passing an argument by reference or by address both enable the passed argument to be changed in the calling function by the called function.
Return pointer from functions	C++ allows a function to return a pointer to local variable, static variable and dynamically allocated memory as well.

These are few important pointer concepts which should be known clearly to a C++ programmer.