Defined in header <iterator> | ||
---|---|---|
template< class BidirIt > BidirIt prev( BidirIt it, typename std::iterator_traits<BidirIt>::difference_type n = 1 ); | (since C++11) (until C++17) | |
template< class BidirIt > constexpr BidirIt prev( BidirIt it, typename std::iterator_traits<BidirIt>::difference_type n = 1 ); | (since C++17) |
Return the n
th predecessor of iterator it
.
it | - | an iterator |
n | - | number of elements it should be descended |
Type requirements | ||
-BidirIt must meet the requirements of BidirectionalIterator. |
The n
th predecessor of iterator it
.
template<class BidirIt> BidirIt prev(BidirIt it, typename std::iterator_traits<BidirIt>::difference_type n = 1) { std::advance(it, -n); return it; } |
Although the expression --c.end()
often compiles, it is not guaranteed to do so: c.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, --c.end()
does not compile, while std::prev(c.end())
does.
#include <iostream> #include <iterator> #include <vector> int main() { std::vector<int> v{ 3, 1, 4 }; auto it = v.end(); auto pv = std::prev(it, 2); std::cout << *pv << '\n'; }
Output:
1
(C++11) | increment an iterator (function) |
advances an iterator by given distance (function) |
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