Dynamic memory allocation allows a program to request memory during runtime.
- Unlike static memory (fixed at compile time), dynamic memory is allocated from the heap.
- This helps manage memory more efficiently, especially for data structures like arrays or linked lists whose size may not be known beforehand.
Why Use Dynamic Memory Allocation?
- To allocate memory when the size of data is unknown or changes during program execution.
- To efficiently manage large or variable-size data.
- To allocate memory for data structures like linked lists, trees, etc.
Functions for Dynamic Memory Allocation:
| Function | Purpose | Header File |
|---|---|---|
malloc() | Allocates specified number of bytes; returns pointer to the first byte. Memory is uninitialized. | <stdlib.h> |
calloc() | Allocates memory for an array of elements, initializes all bytes to zero. | <stdlib.h> |
realloc() | Changes the size of previously allocated memory block. | <stdlib.h> |
free() | Frees the allocated memory, returning it to the system. | <stdlib.h> |
Syntax:
ptr = (castType*) malloc(size_in_bytes);
ptr = (castType*) calloc(num_elements, size_of_element);
ptr = (castType*) realloc(ptr, new_size);
free(ptr);- castType is usually the pointer type you want, e.g., int, float.
- size_in_bytes is typically sizeof(data_type) * number_of_elements.
Example: Allocating and Using Dynamic Array:
#include <stdio.h>
#include <stdlib.h>
int main() {
int *arr;
int n, i;
printf("Enter number of elements: ");
scanf("%d", &n);
// Allocate memory for n integers
arr = (int*) malloc(n * sizeof(int));
if (arr == NULL) {
printf("Memory allocation failed!\n");
return 1;
}
// Initialize array
for (i = 0; i < n; i++) {
arr[i] = i + 1;
}
// Print array elements
printf("Array elements: ");
for (i = 0; i < n; i++) {
printf("%d ", arr[i]);
}
printf("\n");
// Free allocated memory
free(arr);
return 0;
}
