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

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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:

Run this code 
#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)
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