Notes

Two places a variable’s memory can live, with very different rules for how long it sticks around.

Stack

void f() {
    int x = 5;       // lives on the stack
}   // x is automatically destroyed here, no action needed

Fast (just moving a pointer), automatically cleaned up when the scope ends. Limited size — deep recursion or a huge local array can overflow it.

Heap

int* p = new int(5);   // lives on the heap, outlives this function
delete p;                // YOU must say when it's done

Slower to allocate, much bigger capacity, and lives until explicitly freed — or until whatever owns it (a smart pointer, a container) decides to.

Rule of thumb

Default to the stack — automatic and fast. Reach for the heap when something needs to outlive the function that created it, or when its size isn’t known until runtime.

Related

new and delete