🧱 C Pointer to Array – Accessing Entire Arrays via Pointers in C

---

🧲 Introduction – What Is a Pointer to an Array in C?

In C programming, a pointer to an array is a pointer that points to the entire array—not just its first element. Unlike a regular pointer (e.g., int *p), which points to a single element, a pointer to an array (e.g., int (*p)[5]) provides access to the whole array block as a unit.

🎯 In this guide, you’ll learn:

• The syntax of a pointer to an array
• How it’s different from a pointer to the first element
• Examples using both 1D and 2D arrays
• Best practices and practical use cases

---

🔍 Core Concept – Pointer to an Entire Array

When you use int (*ptr)[5];, you’re declaring ptr as a pointer to an array of 5 integers.

✅ Syntax:

int arr[5];
int (*ptr)[5] = &arr;

• ptr holds the address of the whole array block
• *ptr dereferences to the array
• (*ptr)[i] accesses individual elements

---

💻 Code Examples – Pointer to Array in Action

✅ Example 1: Accessing Elements via Array Pointer

#include <stdio.h>

int main() {
    int arr[5] = {10, 20, 30, 40, 50};
    int (*ptr)[5] = &arr;

    for (int i = 0; i < 5; i++) {
        printf("%d ", (*ptr)[i]);
    }

    return 0;
}

🖨️ Output:

10 20 30 40 50

📘 (*ptr)[i] accesses elements from the array that ptr points to.

---

✅ Example 2: Pointer to 2D Array

#include <stdio.h>

int main() {
    int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};
    int (*p)[3] = matrix;  // Points to row arrays of size 3

    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%d ", p[i][j]);
        }
        printf("\n");
    }

    return 0;
}

🖨️ Output:

1 2 3  
4 5 6

📌 p treats matrix as an array of arrays (rows), each of 3 integers.

---

🧩 Pointer to Array vs Array Name vs Pointer to Element

Expression	Meaning
int *p = arr	Pointer to first element (arr[0])
int (*p)[5]	Pointer to the entire array of 5 int
arr	Decays to address of arr[0]
&arr	Address of the whole array

---

💡 Best Practices & Tips

📘 Best Practice:

• Use pointer-to-array when you want to pass an entire array to a function with size context.

💡 Tip:

• Prefer int (*p)[N] over int *p for multi-dimensional arrays or when element grouping matters.

⚠️ Pitfall:

• *p[i] is not the same as (*p)[i]. Always use parentheses to correctly dereference array pointers.

---

🛠️ Real-World Applications

• 📐 Multi-dimensional matrix processing
• 📦 Passing large arrays to functions safely
• 🎮 Game engines (grid maps, tile rendering)
• 🧠 Memory-efficient structure layouts in embedded systems

---

📌 Summary – Recap & Next Steps

Pointers to arrays allow working with entire blocks of memory representing arrays. This enhances control over how data is accessed and manipulated, especially in multi-dimensional scenarios.

🔍 Key Takeaways:

• int (*ptr)[N] is a pointer to an array of N integers
• Use (*ptr)[i] to access array elements
• Different from int *p which only points to the first element
• Vital in 2D array handling and advanced memory management

⚙️ Real-World Relevance:

Used in matrix computation, 2D graphics, firmware memory layouts, and high-performance code.

---

❓ Frequently Asked Questions (FAQ)

❓ What is the difference between int *p = arr and int (*p)[5] = &arr?

✅ int *p points to the first element, while int (*p)[5] points to the entire array as a unit.

---

❓ How do I pass an entire array to a function using a pointer?

✅ Use int (*p)[N] as a parameter and pass the address: func(&arr);

---

❓ Can I use pointer to array with malloc()?

✅ Yes, especially useful for dynamically allocated 2D arrays:

int (*matrix)[cols] = malloc(rows * sizeof(*matrix));

---

❓ Is arr == &arr[0] the same as &arr?

❌ No.

• arr and &arr[0] both point to the first element.
• &arr points to the entire array block.

---

❓ When should I use a pointer to an array?

✅ Use when working with fixed-size blocks, 2D arrays, or when needing size context and tight memory layout.

---

Share Now :