Importance of pointers in C++

Today I found a very helpful article on "programmers.stackexchange.com" regarding the importance of pointers in C++.This article was written by David Thornley.So,I decided to share it with all my readers.

Importance of pointers in C++

Pointers are necessary for dynamic memory location, many data structures, and efficient handling of large amounts of data. Without pointers, you'd have to allocate all the program data globally or in functions or the equivalent, and you'd have no recourse if the amount of data grew beyond what you had originally allowed for. I hesitate to use absolutes here, but as far as I know all modern computer languages have pointers in some form or other.

In most languages that use pointers, there are certain sorts of references that are pointers, and perhaps certain sorts of references that aren't, and there is no further notational difference. A Lisp cons cell is a pair of pointers, although a fixnum is not a pointer. In Java, the variable used for the instance of a class is a pointer, but an int isn't. The language syntax doesn't reflect that.

C is unusual in that pointers are optional, explicit, and allow explicit pointer arithmetic. It is perfectly possible to write struct foo bar; struct foo * baz;, and once you've allocated memory for bazyou can use both bar and baz to represent struct foos. Since pointers are optional, it is useful to have notational differences. (It's essential in C++ for smart pointers, as given boost::shared_ptr<foo> bar;, bar.reset() has one meaning and bar->reset() is likely to have a much different one.)

(Actually, explicit pointers were often used in other languages when C was originally being developed, such as ^ in Pascal. C is an older language than most in common use today, and it shows.)

One of C's design goals was to write Unix in, and therefore it needed to handle memory locations in a detailed manner. (C is actually one of a family of system implementation languages common when it was being designed, another example being Cybol for Control Data computers. C is the one that became a big hit.) Therefore, it is possible to manipulate C pointers directly, assigning memory addresses and calculating new ones. This also led to some design decisions in C. C arrays are based heavily on pointer arithmetic, and indeed an array decays into a pointer in very many situations. Passing variables to C functions by reference is done by pointer. There was no strong need for arrays and passing variables by reference in the form that other contemporary languages had, so C didn't get those.

So, the answer is that, in most languages nowadays, you use pointers constantly without being reminded of the fact. In C, and to a lesser extent C++, you use pointers either to do low-level things, or as accomplish higher-level things that there's no special notation for.

Pointer Declaration in C++

Pointer Declaration

As I have discussed in the previous blog that a pointer is a variable whose value is the address of another variable.Remember that the declaring a pointer is same as declaring a simple variable.An asterisk "*" is used in the declaration that indicates that the variable is a pointer variable.

Syntax

The syntax of declaring a pointer is as follows:

DataType *var;

Example

int *p;

Now,I will demonstrate this concept by a simple program.

Source code

#include<iostream>

#include<conio.h>

using namespace std;

void main( )

{

int n;

int *ptr; // it indicates that "ptr" is a pointer

cout<<"Enter an integer";

cin>>n;

ptr=&n;

cout<<"The value of n:"<<n<<endl;

cout<<"The address of n:"<<ptr<<endl;

getch( );

}

Output

Example of pointers in C++

As we know that a pointer is a variable whose value is the address of another variable. To demonstrate it,consider the following example.

Source code

#include <iostream>

using namespace std;

int main ()

{

   int  var1;

   cout << "Address of var1 variable: ";

   cout << &var1 << endl;

   return 0;

}

Output

Example of pointer

Reference

To know the reference of this blog,

Click here

Concept of pointers in C++

Pointers are an extremely powerful programming tool. They can make some things much easier, help improve your program's efficiency, and even allow you to handle unlimited amounts of data. For example, using pointers is one way to have a function modify a variable passed to it. It is also possible to use pointers to dynamically allocate memory, which means that you can write programs that can handle nearly unlimited amounts of data on the fly--you don't need to know, when you write the program, how much memory you need.      

Concept of pointers

Pointers are aptly named: they "point" to locations in memory. Think of a row of safety deposit boxes of various sizes at a local bank. Each safety deposit box will have a number associated with it so that the teller can quickly look it up. These numbers are like the memory addresses of variables. A pointer in the world of safety deposit boxes would simply be anything that stored the number of another safety deposit box. Perhaps you have a rich uncle who stored valuables in his safety deposit box, but decided to put the real location in another, smaller, safety deposit box that only stored a card with the number of the large box with the real jewelry. The safety deposit box with the card would be storing the location of another box; it would be equivalent to a pointer. In the computer, pointers are just variables that store memory addresses, usually the addresses of other variables. 

Declaration of pointers

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. 

Reference

The reference of this blog is taken from

http://www.cprogramming.com/tutorial/lesson6.html

http://www.tutorialspoint.com/cplusplus/cpp_pointers.htmqq