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

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

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


nsec - the number of nanoseconds

Return value

The std::chrono::duration literal.

Possible implementation

constexpr std::chrono::nanoseconds operator ""ns(unsigned long long ns)
    return std::chrono::nanoseconds(ns);
constexpr std::chrono::duration<long double, std::nano> operator ""ns(long double ns)
    return std::chrono::duration<long double, std::nano>(ns);


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 = 250ns;
    std::chrono::nanoseconds d2 = 1us;
    std::cout << "250ns = " << d1.count() << " nanoseconds\n"
              << "1us = " << d2.count() << " nanoseconds\n";


250ns = 250 nanoseconds
1us = 1000 nanoseconds

See also

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

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