🔴 Advanced · Lesson 33

Dynamic Memory (malloc/free)

Dynamic Memory

Dynamic memory allocation means memory is allocated at run time from the heap. It is useful when the required size is not known before program execution.

Function	Use
`malloc()`	Allocates uninitialized memory
`calloc()`	Allocates zero-initialized memory
`realloc()`	Changes size of allocated memory
`free()`	Releases allocated memory

malloc Example

C Language

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

int main() {
    int n;
    printf("Enter number of students: ");
    scanf("%d", &n);

    int *marks = (int*) malloc(n * sizeof(int));
    if(marks == NULL) {
        printf("Memory allocation failed");
        return 1;
    }

    for(int i = 0; i < n; i++)
        scanf("%d", &marks[i]);

    for(int i = 0; i < n; i++)
        printf("%d ", marks[i]);

    free(marks);
    return 0;
}

calloc Example

C Language

int *arr = (int*) calloc(5, sizeof(int));
for(int i = 0; i < 5; i++)
    printf("%d ", arr[i]);   // all values are 0
free(arr);

realloc Example

C Language

int *arr = (int*) malloc(3 * sizeof(int));
arr = (int*) realloc(arr, 5 * sizeof(int));

free and Common Mistakes

⚠️ Common Mistakes

Forgetting free() causes memory leak
Using pointer after free() is dangling pointer problem
Always check NULL after allocation

Summary

Use dynamic memory when size is known at run time
malloc gives uninitialized memory
calloc initializes memory to zero
realloc changes allocated block size
Always release heap memory using free

Dynamic Memory

Dynamic memory allocation में memory run time पर heap से allocate होती है। जब size पहले से पता न हो, तब यह बहुत useful होती है।

Function	Use
`malloc()`	Uninitialized memory allocate करता है
`calloc()`	Zero-initialized memory allocate करता है
`realloc()`	Memory size बदलता है
`free()`	Memory release करता है

malloc

C Language

int *marks = (int*) malloc(n * sizeof(int));
if(marks == NULL) {
    printf("Memory failed");
    return 1;
}

calloc

C Language

int *arr = (int*) calloc(5, sizeof(int));
// सभी values 0 होंगी
free(arr);

realloc

C Language

arr = (int*) realloc(arr, newSize * sizeof(int));

free और Mistakes

⚠️ सावधानी

free() न करने से memory leak होता है
free() के बाद pointer use न करें
Allocation के बाद NULL check करें

सारांश

Run time size के लिए dynamic memory use करें
malloc uninitialized memory देता है
calloc zero-initialized memory देता है
realloc size change करता है
free memory release करता है

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