Defined in header <chrono>
constexpr std::chrono::milliseconds operator ""ms( unsigned long long ms );
(1) (since C++14)
constexpr std::chrono::duration</*unspecified*/, std::milli>
                                    operator ""ms( long double ms );
(2) (since C++14)

Forms a std::chrono::duration literal representing milliseconds.

1) integer literal, returns exactly std::chrono::milliseconds(ms)
2) floating-point literal, returns a floating-point duration equivalent to std::chrono::milliseconds


ms - the number of milliseconds

Return value

The std::chrono::duration literal.

Possible implementation

constexpr std::chrono::milliseconds operator ""ms(unsigned long long ms)
    return std::chrono::milliseconds(ms);
constexpr std::chrono::duration<long double, std::milli> operator ""ms(long double ms)
    return std::chrono::duration<long double, std::milli>(ms);


This operator is declared in the namespace std::literals::chrono_literals, where both literals and chrono_literals are inline namespaces. Access to this operator can be gained with:

  • using namespace std::literals,
  • using namespace std::chrono_literals, or
  • using namespace std::literals::chrono_literals.

In addition, within the namespace std::chrono, the directive using namespace literals::chrono_literals; is provided by the standard library, so that if a programmer uses using namespace std::chrono; to gain access to the classes in the chrono library, the corresponding literal operators become visible as well.


#include <iostream>
#include <chrono>
int main()
    using namespace std::chrono_literals;
    auto d1 = 250ms;
    std::chrono::milliseconds d2 = 1s;
    std::cout << "250ms = " << d1.count() << " milliseconds\n"
              << "1s = " << d2.count() << " milliseconds\n";


250ms = 250 milliseconds
1s = 1000 milliseconds

See also

constructs new duration
(public member function of std::chrono::duration<Rep,Period>)

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