W3cubDocs

/C++

std::chrono::operator<< (std::chrono::duration)

Defined in header <chrono> 
template<
    class CharT,
    class Traits,
    class Rep,
    class Period
> std::basic_ostream<CharT, Traits>&
    operator<<( std::basic_ostream<CharT, Traits>& os,
                const std::chrono::duration<Rep, Period>& d );
 (since C++20)

Inserts a textual representation of d into os.

Behaves as if it was implemented as.

std::basic_ostringstream<CharT, Traits> s;
s.flags(os.flags());
s.imbue(os.getloc());
s.precision(os.precision());
s << d.count() << units_suffix; // see below
return os << s.str();

In other words, the stream flags, locale, and precision are determined by the stream, but any padding are determined using the entire output string.

The units_suffix is determined based on Period::type according to the following table.

Period::type Suffix
std::atto as
std::femto fs
std::pico ps
std::nano ns
std::micro µs (U+00B5) or us, it is implementation-defined which one is used
std::milli ms
std::centi cs
std::deci ds
std::ratio<1> s
std::deca das
std::hecto hs
std::kilo ks
std::mega Ms
std::giga Gs
std::tera Ts
std::peta Ps
std::exa Es
std::ratio<60> min
std::ratio<3600> h
std::ratio<86400> d
None of the above, and Period::type::den == 1 [num]s
None of the above [num/den]s

For the last two rows of the table, num and den in the suffix are Period::type::num and Period::type::den formatted as a decimal number with no leading zeroes, respectively.

Return value

A reference to the stream, i.e., os.

Example

This example shows the output of std::chrono::operator<< when given a duration:

#include <chrono>
#include <iostream>
using namespace std::chrono_literals;
 
int main()
{
    constexpr auto duration = 123ms;
    std::cout << duration << '\n';
}

Output:

123ms

See also

(C++20)
 stores formatted representation of the arguments in a new string
(function template)
(C++20)
 formatting support for duration
(class template specialization)
performs stream input and output on strings
(function template)
(C++11)
 converts an integral or floating point value to string
(function)
(C++11)
 converts an integral or floating point value to wstring
(function)

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/chrono/duration/operator_ltlt