Dynamic Memory Allocation in C

Introduction

• Discussed dynamic memory allocation concepts in C.
• Focus on library functions: malloc, calloc, realloc, and free.

Memory Basics

• Memory is divided into Stack and Heap.
• Dynamic memory allocation occurs in the Heap section.

Memory Allocation Functions

1. malloc

• Most frequently used function for dynamic memory allocation.
• Signature: void* malloc(size_t size);
• Parameters:
  • Takes one argument: required size in bytes (positive integer).
  • Returns a void pointer to the allocated memory block.
• Usage Example:
  • To allocate memory for an integer: int *p = (int*)malloc(sizeof(int));
• Important:
  • Memory is not initialized (may contain garbage values).

2. calloc

• Similar to malloc, but more specific.
• Signature: void* calloc(size_t num, size_t size);
• Parameters:
  • Takes two arguments: number of elements and size of each element.
  • Initializes allocated memory to zero.
• Usage Example:
  • To allocate memory for an integer array: int *arr = (int*)calloc(n, sizeof(int));

3. realloc

• Used to resize a previously allocated memory block.
• Signature: void* realloc(void* ptr, size_t new_size);
• Parameters:
  • Pointer to the existing block and the new size required.
• Behavior:
  • Can either extend the existing memory block or allocate a new one and copy data.
• Usage Example:
  • int *B = (int*)realloc(A, new_size * sizeof(int));

Memory Deallocation

free

• Frees memory allocated by malloc, calloc, or realloc.
• Usage: free(pointer);
• Important:
  • After freeing, the memory address can still be accessed, but it may lead to undefined behavior.

Code Examples

• Demonstrated how to dynamically allocate memory for arrays based on user input.
• Illustrated differences between malloc and calloc regarding initialization.
• Discussed potential issues with accessing freed memory.

Conclusion

• Emphasized careful memory management in C.
• Future lessons will delve deeper into examples and use cases for dynamic memory allocation.