C++ array of Pointers

Array of Pointers:

In high-level programming languages like C++, the array's name is its pointer. The name of an array contains an address which is the address of an element. In C++, an array name is considered as the address of the first element. For instance, if we have an array of size 20, i.e., it can hold 20 values, then the value will contain the first element's address, i.e., array[0]. Thus, it can be said that name of the array is a pointer that holds the memory address of the first element present in the array.

In other words, an array of pointers is the array consisting of a variable of pointer types. This simply means that the pointer variable is addressing some other elements.

Syntax:     

int *pointer[N];

Here,

 *pointer = pointer array
 N = number of elements or size. 

Example: 

int *ptr[2];

Note: An array of the pointer can also be initialized by assigning the address of the variables like ptr[2] = &a.

There can be various ways of implementing an array of pointers. We may see its application in the arrays and similar data structures like linked-lists, strings, etc. The array of pointers comes in handy while implementing these programming practices efficiently.

To visualize how array of pointer work, let’s look at the below example:

 #include <iostream> 
 using namespace std; 
 int main() 
 { 
     int *pointer;   
     int array[10];
 cout << "Please enter the array elements :" <<endl; 
     for(int i=0;i<10;i++) 
     { 
         cin>>array[i]; 
     } 
     pointer = array;  
                       cout << "The value of *pointer :" <<*pointer<<endl; 
                       cout << "The value of *array :" <<*array<<endl; 
 Return 0;
 }  

Output:

Explanation:

In the above code, we implemented the array of pointers concerning an array that stores elements given by the user. As already discussed above, the array of pointers has the address of the first element of the array. We get the first element printed on the console. Therefore, we declared an integer pointer and integer type array, and we assigned the array to the pointer by equating pointer = array. It means that both have the same element, and the element is at the first index. The values for *pointer and *array will be the same since we have assigned them to be equal.

Let us now look at how the arrays of pointers are used to implement strings using the example code given below.

String application of array pointers:

 #include<bits/stdc++.h>
 using namespace std;
 const int Maximum = 4;
 int main ()
 {
 const char *pandavs[Maximum] = { "Nakul", "Bhim", "Yudhishthir",
                          "Sehdev" };
    for (int i = 0; i < Maximum; i++)
 {
       cout << "Addresses of pandavs: [" << i << "] = ";
       cout << (pandavs + i) << endl;
 }
    return 0;
 } 

Output:

Explanation:

In the above code, we have initialized the value of the array pointer to the maximum. Here, the maximum value can be anything, but to keep it simple and sober, we fixed the size to 4. We have used the const keyword to preserve the value of the maximum to 4. The const keyword is used so that the maximum value or, say, the array's size doesn't increase more than 4. The next step is to loop over the array to access all the values' addresses through the pointer array associated. The addresses of each value are then printed on the console using an array of pointers.

Using array of pointers to print container values:

 #include<bits/stdc++.h>
 using namespace std;
 const int Maximum = 4;
 int main () {
    int  container[Maximum] = {10, 100, 200, 400};
    int *pointer[Maximum];
    for (int i = 0; i < Maximum; i++)
  {
       pointer[i] = &container[i];
   }
    for (int i = 0; i < Maximum; i++) {
       cout << "Value of container at position: [" << i << "] = ";
       cout << *pointer[i] << endl;
  }
    return 0;
 } 

Output:

Explanation:

In the above code, we have used a similar approach as we used in the string example. The value of maximum is constant (cannot be changed) and is kept 4. The only difference in this example is that we have used the container address which holds the integers. The next step is to iterate over the elements and by doing that we now know that each element in ptr, now holds a pointer to an int value.

The output generated is the values at their respective indexes.

Let us now look at some of the applications of array of pointers.

Applications

1. The array of pointers comes in handy while making embedded systems. A temperature measuring system may need to scale up different sensors so we can use an array of pointers to hold the memory address of each sensor so that it will be very easy to manipulate the sensor status.

• An array of pointers allows us to numerically index a large set of variables.

• We can separately make pointer variables that can point to different values or we can make one integer array of pointers to point all the values.