Memory-in-c-programming-language-

How memory in c works

📌 Memory in C Programming

C programming provides low-level access to memory, which makes it powerful but also risky if not used carefully. Understanding memory management and pointers is crucial for efficient and bug-free C programs.

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1️⃣ Memory Layout of a C Program

When a C program runs, memory is divided into different segments:

1. Text Segment (Code Segment)

Stores compiled machine instructions.

Usually read-only (prevents modifying instructions at runtime).

2. Data Segment

Stores global and static variables.

Divided into:

Initialized Data Segment → variables with defined values.

Uninitialized Data Segment (BSS) → variables initialized to zero or left uninitialized.

3. Heap

Used for dynamic memory allocation (malloc, calloc, realloc, free).

Grows upwards (towards higher memory addresses).

4. Stack

Used for function calls, local variables, and return addresses.

Grows downwards (towards lower memory addresses).

📌 Example:

High Address +-------------------+ | Command-line | | Arguments | +-------------------+ | Stack | <--- grows downward +-------------------+ | Heap | <--- grows upward +-------------------+ | Uninitialized | | Data (BSS) | +-------------------+ | Initialized | | Data | +-------------------+ | Code | +-------------------+ Low Address

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2️⃣ Pointers in C

A pointer is a variable that stores the memory address of another variable.

Syntax:

int a = 10; int *p = &a; // p stores address of a

Important Operators:

& → Address-of operator (gets memory address).

• → Dereference operator (access value at the address).

📌 Example:

#include <stdio.h> int main() { int x = 42; int *ptr = &x;

printf("Value of x: %d\n", x);
printf("Address of x: %p\n", &x);
printf("Value stored in ptr: %p\n", ptr);
printf("Value pointed by ptr: %d\n", *ptr);

return 0;

}

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3️⃣ Types of Pointers

1. Null Pointer → Points to nothing.

int *p = NULL;

2. Void Pointer → Generic pointer (can store address of any type).

void *ptr;

3. Dangling Pointer → Points to freed or invalid memory.

int *p; { int x = 10; p = &x; } // x goes out of scope → p becomes dangling

4. Wild Pointer → Uninitialized pointer (random address).

int *p; // not initialized

5. Function Pointer → Points to a function.

int add(int a, int b) { return a+b; } int (*fp)(int, int) = &add;

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4️⃣ Pointer Arithmetic

Pointers can be incremented/decremented to move across memory addresses.

Example:

int arr[3] = {10, 20, 30}; int *p = arr;

printf("%d\n", *p); // 10 p++; printf("%d\n", *p); // 20

📌 Note: Increment depends on data type size.

int *p → moves by 4 bytes (on 32-bit system).

char *p → moves by 1 byte.

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5️⃣ Dynamic Memory Allocation

C provides library functions (stdlib.h) for heap memory management:

1. malloc() → Allocates uninitialized memory.

int p = (int) malloc(5 * sizeof(int));

2. calloc() → Allocates zero-initialized memory.

int p = (int) calloc(5, sizeof(int));

3. realloc() → Resizes previously allocated memory.

p = (int*) realloc(p, 10 * sizeof(int));

4. free() → Frees allocated memory.

free(p);

⚠️ Always free() dynamically allocated memory to prevent memory leaks.

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6️⃣ Memory Issues in C

1. Memory Leak → Forgetting to free memory.

2. Segmentation Fault → Accessing invalid memory.

3. Dangling Pointers → Using freed/unavailable memory.

4. Buffer Overflow → Writing outside allocated memory.

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7️⃣ Example Program (Dynamic Array with Pointers)

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

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

int *arr = (int*) malloc(n * sizeof(int));

if(arr == NULL) {
    printf("Memory allocation failed!\n");
    return 1;
}

printf("Enter elements:\n");
for(i = 0; i < n; i++) {
    scanf("%d", &arr[i]);
}

printf("You entered:\n");
for(i = 0; i < n; i++) {
    printf("%d ", arr[i]);
}

free(arr); // release memory
return 0;

}

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8️⃣ Key Takeaways

Memory in C is divided into Code, Data, Heap, and Stack.

Pointers are used to directly access memory addresses.

Proper use of malloc/calloc/realloc/free is essential.

Always watch out for dangling pointers and memory leaks.