std::distance

 

C++

Language

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Utilities library

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Iterators library

Numerics library

Input/output library

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Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Iterator library

Iterator primitives
iterator_traits
input_iterator_tag output_iterator_tag forward_iterator_tag bidirectional_iterator_tag random_access_iterator_tag
iterator
Iterator adaptors
reverse_iterator
move_iterator (C++11) back_insert_iterator front_insert_iterator insert_iterator	make_move_iterator (C++11) back_inserter front_inserter inserter
Stream iterators
istream_iterator
ostream_iterator
istreambuf_iterator
ostreambuf_iterator
Iterator operations
advance
distance
prev (C++11)
next (C++11)
Range access
begin (C++11)
end (C++11)

 

Defined in header <iterator>
template< class InputIt > typename std::iterator_traits<InputIt>::difference_type     distance( InputIt first, InputIt last );

Returns the number of elements between first and last.

The behavior is undefined if last is not reachable from first by (possibly repeatedly) incrementing first.

Parameters

first	-	iterator pointing to the first element
last	-	iterator pointing to the last element
Type requirements
- InputIt must meet the requirements of InputIterator. The operation is more efficient if InputIt additionally meets the requirements of RandomAccessIterator

Return value

The number of elements between first and last.

Complexity

Linear.

However, if InputIt additionally meets the requirements of RandomAccessIterator, complexity is constant.

Example

run this code

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

Output:

3

See also

advance	advances an iterator by given distance (function)