C Pointers Application
The following are some major applications of pointers in the C programming language:
1. Passing Arguments by Reference
Passing arguments by reference serves two purposes:
i.) to modify the variable in another function.
Example
The below example demonstrates the use of pointers by swapping two numbers.
// C program to demonstrate that we can change
// local values of one function in another using pointers.
#include <stdio.h>
void swap(int* x, int* y)
{
int temp = *x;
*x = *y;
*y = temp;
}
int main()
{
int x = 10, y = 20;
swap(&x, &y);
printf("%d %d\n", x, y);
return 0;
}
Output
20 10
ii.) For Efficiency Purpose
Example
The below example demonstrates the use of pointers to write efficient code.
#include <stdio.h>
// function to print an array by passing reference to array
void printArray(int* arr, int n)
{
// here array elements are passed by reference
for (int i = 0; i < n; i++) {
printf("%d ", arr[i]);
}
}
int main()
{
int arr[5] = { 1, 2, 3, 4, 5 };
printArray(arr, 5);
return 0;
}
Output
1 2 3 4 5
Note: Passing large structure without reference would create a copy of the structure (hence wastage of space).
2. For Accessing Array Elements
Compiler internally uses pointers to access array elements. We can also use these pointers to access and modify the elements of the given array.
Example
The below example demonstrate the use of pointers to access elements of an array.
// C program to demonstrate that compiler
// internally uses pointer arithmetic to access
// array elements.
#include <stdio.h>
int main()
{
int arr[] = { 100, 200, 300, 400 };
// Compiler converts below to *(arr + 2).
printf("%d ", arr[2]);
// So below also works.
printf("%d\n", *(arr + 2));
return 0;
}
Output
300 300
3. To Return Multiple Values
The functions in C can only return a single value, but we can use pointers to return multiple values from a C function.
Example
The below example demonstrates the use of pointers to return square and square root of numbers using pointers.
// C program to demonstrate that using a pointer
// we can return multiple values.
#include <math.h>
#include <stdio.h>
void fun(int n, int* square, double* sq_root)
{
*square = n * n;
*sq_root = sqrt(n);
}
int main()
{
int n = 100;
int sq;
double sq_root;
fun(n, &sq, &sq_root);
printf("%d %f\n", sq, sq_root);
return 0;
}
Output:
10000
10
4. For dynamic memory Allocation
We can use pointers to dynamically allocate memory i.e Dynamic memory allocation. The advantage of dynamically allocated memory is, it is not deleted until we explicitly delete it.
Example
The below example shows the use of pointers to dynamically allocate memory.
// C program to dynamically allocate an
// array of given size.
#include <stdio.h>
#include <stdlib.h>
int* createArr(int n)
{
int* arr = (int*)(malloc(n * sizeof(int)));
return arr;
}
int main()
{
int* pt = createArr(10);
return 0;
}
Applications of Pointers in C
Pointers in C are variables that are used to store the memory address of another variable. Pointers allow us to efficiently manage the memory and hence optimize our program. In this article, we will discuss some of the major applications of pointers in C.
Prerequisite: Pointers in C.