CODE: C CPP Memory

What Is Memory

Memory is the physical storage where a program’s instructions, data, and state live while it runs.

The CPU does not “see” variables or objects.

It sees addresses and bytes.

Everything in C and C++—variables, arrays, objects, stacks, heaps—exists only as:

• a memory address
• a size
• a lifetime

Understanding memory allocation is therefore not an “advanced topic” — it is the foundation of correct, fast, and safe software.

The Process Memory Layout

A typical C/C++ program is divided into regions:

This naturally leads to two fundamental allocation models:

1. Static allocation (Compile time)
2. Dynamic allocation (Run time)

Choosing _how_ memory is allocated directly affects:

• Performance
• Determinism
• Safety
• Cache behavior
• Fragmentation
• Scalability

Rule of thumb:

Memory mistakes in C/C++ don’t fail loudly — they fail silently.

So let’s start where memory begins.

Static Memory Allocation

it is the data in Data, BSS memory segments.

Static memory allocation means:

• Memory size is known at compile time
• Memory address is fixed
• Memory lifetime is entire program execution

No runtime decision.

No allocation overhead.

No failure.

Use static allocation when:

• Size is known and fixed
• Lifetime spans the whole program
• Determinism is required (embedded / RTOS)
• Performance is critical
• Memory must never fail

Static Allocation in C

Global Variables

int global_counter = 0;

• Allocated in Data segment
• Exists from program start to exit

Static Global (Internal Linkage)

static int file_private_counter;

• Visible only in this translation unit
• Still static lifetime

Static Local Variables

void increment(void) {
    static int count = 0;
    count++;
    printf("%d\n", count);
}

Why this exists:

To preserve state across function calls without heap allocation.

Static Arrays

static int buffer[1024];

• Fixed size
• Fast access
• Zero fragmentation

Stack Allocation in C

assigned variables

int a = 5;

pointers: which is a variable that stores the memory address.

Wild pointer: the un-intilized pointer.

void *ptr;

Null pointer: pointer points to nothing = null or 0

void *ptr = ((void *)0);
void *ptr = NULL;

Dangling Pointer: when the object deleted or de-allocated, and the pointer still exist.

Static Allocation in C++

C++ adds object lifetime semantics on top.

Static Objects

struct Logger {
    Logger() { std::cout << "Init\n"; }
    ~Logger() { std::cout << "Destroy\n"; }
};

static Logger logger;

• Constructor runs before main()
• Destructor runs after main()
• Order across translation units is not guaranteed

> Static Initialization Order Fiasco, This problem alone is why large C++ systems avoid global statics.

Why Static Allocation Is Fast:

• No system calls
• No locks
• No bookkeeping
• Perfect cache locality
• Zero fragmentation

But nothing is free.

Limitations of Static Allocation

Static memory cannot:

• Grow or shrink
• Be conditionally created
• Be freed early
• Handle unknown sizes

So what happens when size or lifetime is not known?

We move to dynamic allocation.

Dynamic Memory Allocation

Dynamic allocation means:

• Memory size decided at runtime
• Memory taken from the heap
• Lifetime controlled manually

This gives flexibility — but introduces risk.

You need dynamic allocation when:

• Size depends on input or runtime state
• Lifetime exceeds a single scope
• Objects must outlive function calls
• Data structures grow (lists, trees, maps)

Dynamic Allocation in C

malloc

Allocate memory from heap but does not initialize it.

int* arr = (int*)malloc(10 * sizeof(int));
if (arr == NULL) {
	printf("Memory allocation failed\n");
	return 1;
}

• Uninitialized memory
• Fast but dangerous

calloc

Allocate memory from heap and initializes it to 0

int* arr = (int*)calloc(10, sizeof(int));

• Zero-initialized
• Slightly slower

realloc

Resize an existing allocated memory block which is already allocated before.

arr = realloc(arr, 20 * sizeof(int));

• May move memory
• Pointer may change
• Old pointer invalid if moved

free

free(arr);
arr = NULL;

Every `malloc` must have **exactly one** `free`.

Dynamic Allocation in C++

new

// Single Object
int* p = new int(42); // 42 is initial value
delete p;

// Array
int* arr = new int[10];
delete[] arr;