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std::chrono::duration<Rep,Period>:: operator++, std::chrono::duration<Rep,Period>:: operator--

From cppreference.net
C++
Date and time library
std::chrono::duration
Member functions
Non-member functions
Helper classes
duration & operator ++ ( ) ;
(1) (since C++11)
(constexpr since C++17)
duration operator ++ ( int ) ;
(2) (since C++11)
(constexpr since C++17)
duration & operator -- ( ) ;
(3) (since C++11)
(constexpr since C++17)
duration operator -- ( int ) ;
(4) (since C++11)
(constexpr since C++17)

Increments or decrements the number of ticks for this duration.

If rep_ is a member variable holding the number of ticks in a duration object,

1) Equivalent to ++ rep_ ; return * this ; .
2) Equivalent to return duration ( rep_ ++ ) .
3) Equivalent to -- rep_ ; return * this ; .
4) Equivalent to return duration ( rep_ -- ) ; .

Contents

Parameters

(none)

Return value

1,3) A reference to this duration after modification.
2,4) A copy of the duration made before modification.

Example

Run this code 
#include <chrono>
#include <iostream>
int main()
{
    std::chrono::hours h(1);
    std::chrono::minutes m = ++h;
    m--;
    std::cout << m.count() << " minutes\n";
}

Output: 

119 minutes

See also

implements compound assignment between two durations
(public member function)
(C++11)
implements arithmetic operations with durations as arguments
(function template)