# <chrono>

**[<chrono>](https://en.cppreference.com/w/cpp/header/chrono)** provides time utilities: `std::chrono::system_clock` (wall time), `std::chrono::steady_clock` (monotonic, never goes backwards), and `std::chrono::high_resolution_clock` (highest precision available). You work with `duration` (a time interval) and `time_point` (a specific moment).

For benchmarking or measuring elapsed time, always use `steady_clock`. For absolute dates, use `system_clock`.

## Example

This example measures the elapsed time of a sleep operation using `steady_clock` and converts the duration to milliseconds.

```cpp
// compile: g++ -std=c++11 -o chronoexample chronoexample.cpp
// run: ./chronoexample
// description: measure elapsed time

#include <chrono>
#include <iostream>
#include <thread>

int main() {
    auto start = std::chrono::steady_clock::now();
    
    std::this_thread::sleep_for(std::chrono::milliseconds(100));
    
    auto end = std::chrono::steady_clock::now();
    auto elapsed_ms = std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
    
    std::cout << "elapsed: " << elapsed_ms.count() << " ms\n";
    
    return 0;
}
```