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Showing content from https://en.cppreference.com/w/cpp/language/../error/error_code/../../iterator/ranges/prev.html below:

std::ranges::prev - cppreference.com

Return the n^th predecessor of iterator i.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

Explicit template argument lists cannot be specified when calling any of them.
None of them are visible to argument-dependent lookup.
When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

[edit] Parameters i - an iterator n - number of elements i should be descended bound - iterator denoting the beginning of the range i points to [edit] Return value

1) The predecessor of i.

2) The n^th predecessor of iterator i.

3) The n^th predecessor of iterator i, or the first iterator that compares equal to bound, whichever is first.

[edit] Complexity

1) Constant.

[edit] Possible implementation [edit] Notes

Although the expression --r.end() often compiles for containers, it is not guaranteed to do so: r.end() is an rvalue expression, and there is no iterator requirement that specifies that decrement of an rvalue is guaranteed to work. In particular, when iterators are implemented as pointers or its operator-- is lvalue-ref-qualified, --r.end() does not compile, while ranges::prev(r.end()) does.

This is further exacerbated by ranges that do not model ranges::common_range. For example, for some underlying ranges, ranges::transform_view::end doesn't have the same return type as ranges::transform_view::begin, and so --r.end() won't compile. This isn't something that ranges::prev can aid with, but there are workarounds.

[edit] Example

#include <iostream>
#include <iterator>
#include <vector>
 
int main() 
{
    std::vector<int> v{3, 1, 4};
    auto pv = std::ranges::prev(v.end(), 2);
    std::cout << *pv << '\n';
 
    pv = std::ranges::prev(pv, 42, v.begin());
    std::cout << *pv << '\n';
}

Output:

[edit] See also increment an iterator by a given distance or to a bound
(algorithm function object)[edit] advances an iterator by given distance or to a given bound
(algorithm function object)[edit] decrement an iterator
(function template) [edit]

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