How to Dynamically Grow an Array or Pointer in C at Runtime

Learn how to dynamically resize arrays in C using pointers while managing memory, without predefined lengths at compile time.
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How to Dynamically Grow an Array or Pointer in C at Runtime

Dealing with arrays in C can be challenging, especially when you don't know in advance how many elements you need to store. This guide will discuss how to dynamically grow an array or a pointer in C at runtime, providing you with a flexible approach for managing memory. Let’s tackle this problem step-by-step.

Understanding the Problem

When you need to hold a variable number of items in an array, one common question arises:

Is it possible to grow an array in C at runtime?

The short answer is no. Once an array is defined in C, its size cannot change. However, we can use a pointer-based approach to work around this limitation.

Solution: Using Pointers Instead of Arrays

Step 1: Declaring a Pointer

Instead of using a static array, we will declare a pointer that can point to an int. This pointer will allow us to allocate memory dynamically based on our needs at runtime.

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Step 2: Growing the Array

To grow the array, we will use the realloc() function. This function allows us to resize the memory block pointed to by the pointer. Here’s how it works:

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n is the current number of elements in your array.

The sizeof *arr determines the amount of memory needed for the type of elements being stored (in this case, int).

Step 3: Adding New Elements

After reallocating memory, we can add new values to our dynamically allocated array:

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Step 4: Printing the Values

To print the current value, you should reference the latest inserted element and not the first element each time. Adjust the printf statement as follows:

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Complete Working Example

Combining all the above steps, here's a complete example:

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Key Points to Remember

Dynamic Memory: Use pointers and functions like malloc and realloc to manage memory dynamically.

Array Limitation: Regular arrays have a fixed size and cannot be resized once defined.

Memory Management: Always remember to free the dynamically allocated memory to avoid memory leaks.

Conclusion

Dynamic memory management in C using pointers is a powerful technique that grants you flexibility with arrays. By following the steps outlined in this guide, you can effectively grow your arrays at runtime without knowing in advance how many elements you need.

By understanding these principles, you'll be well on your way to mastering dynamic memory management in C!