C++ Pointer Arithmetic

In this page:

Incrementing a Pointer
Decrementing a Pointer
Adding and Subtracting Integers
Subtracting Two Pointers
Comparing Pointers

Incrementing a Pointer

Incrementing a pointer with ptr++ doesn't simply add 1 to the raw address value — it advances the pointer by exactly the size, in bytes, of the type it points to, so an int* moves forward 4 bytes while a double* moves forward 8. This is precisely what makes ptr++ correctly land on the next element of an array rather than the middle of the current one.

Example: Incrementing a Pointer

cpp

#include <iostream>

int main() {
	int arr[] = {10, 20, 30};
	int *ptr = arr;
	ptr++;
	std::cout << *ptr << std::endl;
	return 0;
}

Decrementing a Pointer

Decrementing with ptr-- works the same way in reverse, stepping the pointer backward by one full element's worth of bytes rather than by a single raw byte, which is essential for walking backward through an array correctly.

Example: Decrementing a Pointer

cpp

#include <iostream>

int main() {
	int arr[] = {10, 20, 30};
	int *ptr = &arr[2];
	ptr--;
	std::cout << *ptr << std::endl;
	return 0;
}

Adding and Subtracting Integers

Adding or subtracting an integer n directly, like ptr + n, moves the pointer forward or backward by n full elements at once rather than n raw bytes — this is how you can jump straight to the fifth element of an array with ptr + 4 instead of incrementing one step at a time in a loop.

Example: Adding and Subtracting Integers

cpp

#include <iostream>

int main() {
	int arr[] = {10, 20, 30, 40};
	int *ptr = arr;
	std::cout << *(ptr + 2) << std::endl;
	return 0;
}

Subtracting Two Pointers

Subtracting one pointer from another of the same type, like ptr2 - ptr1, gives you the number of elements separating them, not the raw byte distance — this is exactly how the standard library computes distances between iterators pointing into the same array or container.

Example: Subtracting Two Pointers

cpp

#include <iostream>

int main() {
	int arr[] = {10, 20, 30, 40};
	int *ptr1 = &arr[0];
	int *ptr2 = &arr[3];
	std::cout << ptr2 - ptr1 << std::endl;
	return 0;
}

Comparing Pointers

Pointers into the same array can be compared with <, >, and == to check their relative positions, which is a common technique for detecting when a pointer has reached the end of an array (ptr == arr + size) or for controlling loops that walk a range using pointers instead of indices.

Example: Comparing Pointers

cpp

#include <iostream>

int main() {
	int arr[] = {10, 20, 30};
	int *ptr1 = &arr[0];
	int *ptr2 = &arr[2];
	if (ptr1 < ptr2) {
		std::cout << "ptr1 comes before ptr2" << std::endl;
	}
	return 0;
}

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