Pointers:

Pointers are useful in manipulating computer memory thus simplifies many tasks in programming, such as sorting arrays; however, the actual benefits of pointers are beyond the scope of this tutorial. Nevertheless, it is still useful to get a glimpse of what they are, and what they basically do. As the name implies, a pointer acts as a reference point to memory. In fact, the seekg() and seekp() functions you saw in the file stream section were pointer functions that point to a specific location in a file loaded into memory. For now note the use of the asterisk ‘*’ and ampersand ‘&’.

Okay, let’s go over some basic concepts of pointers with the following example:

…

int *ptr;                      //ptr is now a pointer variable, note the use of ‘*’
int x = 3;                      
ptr = &x;       //&x gives the memory address of x instead of the value it holds
                    //now pointer ptr points directly to x in memory
cout << ptr << endl;    //outputs the memory address, something similar to this:                                   //0x0064fe00 which is also the address of &x
cout << *ptr << endl;      //outputs the value that address holds, which is 3
*ptr += 3;                      //add 3 to itself through dereferencing
cout << *ptr << endl;             //now the value becomes 6

…

One way to use pointers is to pass function parameters by reference. For example:

#include <iostream.h>

void sum(int x, int y, int &sum)
{
      sum=x+y;
}

int main()
{
     int sum;
     sum(4,7,sum);
     cout << sum;
     return 0;
}

In this example, even though the value of sum is not returned by the function, the void sum() function makes direct change to the memory location of variable sum in the main function, because it is passed to void sum() by reference. Passing by reference is often used to save computer memory on big arguments like an array or a matrix. The const

statement is sometimes used to make sure variables passed by reference are not modified by the function, when they are not meant to be modified. Such as:

int sum(const int &x, const int &y, int &sum)

Now no matter what you do to x and y within the function, you cannot change x and y in any way.

For this tutorial, that’s about it for pointers, if you are serious about learning pointers, which is important in advance C++ programming, please check our reference page for more information.

THE END