How to use use an array of pointers (Jagged) in C/C++?

In C programming, an array of pointers (also known as jagged arrays) allows you to store multiple pointers in a single array. This is particularly useful when working with strings of different lengths or when you need to point to different memory locations dynamically.

Syntax

data_type *array_name[size];

Where data_type is the type of data the pointers will point to, and size is the number of pointers the array can hold.

Example 1: Array of Integer Pointers

The following example demonstrates how to create an array of pointers that point to integer values −

#include <stdio.h>

const int MAX = 3;

int main() {
    int var[] = {10, 100, 200};
    int *ptr[MAX];
    int i;
    
    /* Assign addresses of integers to pointer array */
    for (i = 0; i < MAX; i++) {
        ptr[i] = &var[i];
    }
    
    /* Access values through pointer array */
    for (i = 0; i < MAX; i++) {
        printf("Value of var[%d] = %d\n", i, *ptr[i]);
    }
    
    return 0;
}

Value of var[0] = 10
Value of var[1] = 100
Value of var[2] = 200

Example 2: Array of Character Pointers (Strings)

Arrays of character pointers are commonly used to store multiple strings efficiently −

#include <stdio.h>

const int MAX = 4;

int main() {
    char *names[] = {
        "Zara Ali",
        "Hina Ali", 
        "Nuha Ali",
        "Sara Ali"
    };
    int i;
    
    for (i = 0; i < MAX; i++) {
        printf("Value of names[%d] = %s\n", i, names[i]);
    }
    
    return 0;
}

Value of names[0] = Zara Ali
Value of names[1] = Hina Ali
Value of names[2] = Nuha Ali
Value of names[3] = Sara Ali

Example 3: Dynamic Memory Allocation with Pointer Arrays

You can also use pointer arrays with dynamically allocated memory −

#include <stdio.h>
#include <stdlib.h>

int main() {
    int *ptr[3];
    int values[] = {25, 50, 75};
    int i;
    
    /* Allocate memory and assign values */
    for (i = 0; i < 3; i++) {
        ptr[i] = (int*)malloc(sizeof(int));
        if (ptr[i] != NULL) {
            *ptr[i] = values[i];
        }
    }
    
    /* Display values */
    for (i = 0; i < 3; i++) {
        if (ptr[i] != NULL) {
            printf("Value %d: %d\n", i, *ptr[i]);
        }
    }
    
    /* Free allocated memory */
    for (i = 0; i < 3; i++) {
        if (ptr[i] != NULL) {
            free(ptr[i]);
        }
    }
    
    return 0;
}

Value 0: 25
Value 1: 50
Value 2: 75

Key Points

• Each element in a pointer array stores a memory address, not the actual value.
• Use the dereference operator (*) to access the value at the address.
• Pointer arrays are memory-efficient for storing strings of varying lengths.
• Always check for NULL when using dynamic memory allocation.
• Remember to free dynamically allocated memory to prevent memory leaks.

Conclusion

Array of pointers in C provides flexibility for handling multiple data elements efficiently. They are particularly useful for string arrays and dynamic memory management, offering better memory utilization compared to traditional 2D arrays.