std::prev

Since C++17

Header: <iterator>

Return the nth predecessor (or -nth successor if n is negative) of iterator it.

# Declarations

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)

# Parameters

it: an iterator
n: number of elements it should be descended

# Return value

An iterator of type BidirIt that holds the nth predecessor (or -nth successor if n is negative) of iterator it.

# 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 or its operator– is lvalue-ref-qualified, –c.end() does not compile, while std::prev(c.end()) does.

# 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';
 
    it = v.begin();
    pv = std::prev(it, -2);
    std::cout << *pv << '\n';
}