std::vector memory management:
┌──────────────┬───────────────────────────────┬────────────────────────┐
│ [0] [1] [2] │ (Unused Allocated Storage) │ │
└──────────────┴───────────────────────────────┴────────────────────────┘
▲ ▲ ▲
begin() size() / end() capacity()push_back(v) / emplace_back(args...): Amortized $O(1)$ append.reserve(n): Allocates capacity in advance without creating elements.shrink_to_fit(): Frees unused extra capacity.#include <iostream>
#include <vector>
int main() {
std::vector<int> vec;
vec.reserve(5); // Pre-allocate memory for 5 elements
std::cout << "Initial: Size = " << vec.size() << ", Capacity = " << vec.capacity() << "\n";
for (int i = 1; i <= 6; ++i) {
vec.push_back(i * 10);
std::cout << "Added " << i * 10 << " -> Size: " << vec.size()
<< ", Capacity: " << vec.capacity() << "\n";
}
std::cout << "Elements: ";
for (int val : vec) std::cout << val << " ";
std::cout << "\n";
return 0;
}reserve() whenever the approximate number of items is known to eliminate multiple reallocations.emplace_back() instead of push_back() for non-primitive objects..at(index) when bounds-checking is required, or operator[] for maximum speed in verified loops.