Lære Stack vs Heap | Dynamic Allocation and Multi-level Pointers

Definition

The stack and heap are two main memory regions where a C program stores data during execution. The stack handles automatic variables, while the heap is used for manually allocated memory.

Understanding how these two areas work is important before learning dynamic memory allocation. Each region has its own rules and purposes, affecting how you use variables, pointers, and memory in your programs. Knowing the difference helps you write safer and more efficient C code.

Stack Memory

Stack memory is automatically managed by your program. It is used for local variables and function calls. When you declare a variable inside a function, it is stored on the stack. This memory management is:

Fast and efficient;
Limited in size and fixed when the program starts;
Released automatically when a function ends.

You do not need to manually allocate or free stack memory. Once a function finishes, all local variables stored on the stack are removed, ensuring that memory is efficiently recycled for the next function call.

Heap Memory

Heap memory is a region of memory that you manage manually as a programmer. You use the heap for dynamic memory allocation, which allows you to request memory during the execution of your program using functions like malloc, calloc, or realloc. Key characteristics of heap memory:

Memory is allocated and freed manually by the programmer;
Used for dynamic data structures such as linked lists, trees, and large arrays whose size may not be known at compile time;
Accessing heap memory is generally slower than stack memory due to extra bookkeeping and the need to search for free memory blocks;
The heap can grow in size until the available system memory is exhausted;
You must release heap memory explicitly using the free function to avoid memory leaks.

Heap memory provides flexibility for complex and scalable programs, but it also requires careful management to ensure efficient and safe use of resources.

main.c


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#include <stdio.h>

int main() {
    int a = 10;              // `a` is stored on the stack
    int arr[5] = {1, 2, 3, 4, 5}; // `arr` is stored on the stack

    printf("Value of a: %d\n", a);
    printf("Values in arr: ");
    for (int i = 0; i < 5; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");

    return 0;
}

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