< cpp‎ | iterator
Defined in header <iterator>
template< class BidirIt >

BidirIt prev( BidirIt it,

              typename std::iterator_traits<BidirIt>::difference_type n = 1 );
(since C++11)

Return the nth predecessor of iterator it.


[edit] Parameters

it - an iterator
n - number of elements it should be descended
Type requirements
BidirIt must meet the requirements of BidirectionalIterator.

[edit] Return value

The nth predecessor of iterator it.

[edit] Possible implementation

template<class BidirIt>
BidirIt prev(BidirIt it, typename std::iterator_traits<BidirIt>::difference_type n = 1)
    std::advance(it, -n);
    return it;

[edit] Notes

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.

[edit] Example

#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';



[edit] See also

increment an iterator
advances an iterator by given distance