NAME

std::chrono::duration::operator= - std::chrono::duration::operator=

Synopsis

duration& operator=( const duration &other ) = default; (since C++11)

Assigns the contents of one duration to another.

Parameters

other - duration to copy from

Example

// Run this code

#include <iostream>
#include <chrono>

int main()
{
using namespace std::chrono_literals;

std::chrono::hours z_hours{};
std::chrono::seconds z_seconds{};

z_hours = 2h; // ok, no conversion needed

z_seconds = z_hours;
// First, the converting ctor is used to create a temporary object of `lhs`s type.
// This ctor implicitly invokes the casting function
// chrono::duration_cast<std::seconds>(z_hours). The resulting `rhs` rvalue
// has the same type as `lhs`, and the `operator=` finally performs the assignment.

std::cout << "hours: " << z_hours.count() << '\n';
std::cout << "seconds: " << z_seconds.count() << '\n';

z_seconds -= 42s;

// z_hours = z_seconds; // compile-time error (which is good): incompatible types.
// The library avoids the implicit cast to prevent a potential precision loss.

z_hours = std::chrono::duration_cast<std::chrono::hours>(z_seconds); // ok
z_hours = std::chrono::duration_cast<decltype(z_hours)>(z_seconds); // ditto

std::cout << "hours: " << z_hours.count() << '\n';
std::cout << "seconds: " << z_seconds.count() << '\n';

std::chrono::duration<double, std::ratio<3600>> z2_hours{};

z2_hours = z_seconds; // ok, no truncation, implicit cast

std::cout << "hours: " << z2_hours.count() << '\n';
}

Output:

hours: 2
seconds: 7200
hours: 1
seconds: 7158
hours: 1.98833

See also

constructor constructs new duration
(public member function)