std::ranges::subrange<I,S,K>:: advance

Increments or decrements begin_ :

• If I models bidirectional_iterator and n < 0 is true , decrements begin_ by - n elements. Equivalent to:

ranges:: advance ( begin_  , n ) ;
if constexpr ( StoreSize  )
size_ + = to-unsigned-like  ( - n ) ;
return * this ; .

• Otherwise, increments begin_ by n elements, or until end_ is reached. Equivalent to:

auto d = n - ranges:: advance ( begin_  , n, end_  ) ;
if constexpr ( StoreSize  )
size_ - = to-unsigned-like  ( d ) ;
return * this ; .

According to the preconditions of ranges::advance , if n < 0 is true and begin_ cannot be decremented by - n elements, the behavior is undefined.

Parameters

Return value

* this

Example

#include <algorithm>
#include <array>
#include <iostream>
#include <iterator>
#include <ranges>
 
void print(auto name, auto const sub)
{
    std::cout << name << ".size() == " << sub.size() << "; { ";
    std::ranges::for_each(sub, [](int x) { std::cout << x << ' '; });
    std::cout << "}\n";
};
 
int main()
{
    std::array arr{1, 2, 3, 4, 5, 6, 7};
    std::ranges::subrange sub{std::next(arr.begin()), std::prev(arr.end())};
    print("1) sub", sub);
    print("2) sub", sub.advance(3));
    print("3) sub", sub.advance(-2));
}

1) sub.size() == 5; { 2 3 4 5 6 }
2) sub.size() == 2; { 5 6 }
3) sub.size() == 4; { 3 4 5 6 }

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also