std::distance
STD：：距离
| Defined in header | | |
|---|---|---|
| template< class InputIt > typename std::iterator_traits<InputIt>::difference_type distance( InputIt first, InputIt last | | (until C++17) |
| template< class InputIt > constexpr typename std::iterator_traits<InputIt>::difference_type distance( InputIt first, InputIt last | | (since C++17) |
返回跳数。first到last...
参数
| The behavior is undefined if last is not reachable from first by (possibly repeatedly) incrementing first. | (until C++11) |
|---|---|
| If InputIt is not RandomAccessIterator, the behavior is undefined if last is not reachable from first by (possibly repeatedly) incrementing first. If InputIt is RandomAccessIterator, the behavior is undefined if last is not reachable from first and first is not reachable from last. | (since C++11) |
| first | - | iterator pointing to the first element |
|---|---|---|
| last | - | iterator pointing to the end of the range |
类型要求
-输入必须符合输入器的要求。如果InputIt能满足RandomAccessIterator的要求，则操作效率更高。
返回值
需要增加的数目first到last如果使用随机访问迭代器，则值可能为负值first可从last%28自C++11%29。
复杂性
线性的。
但是，如果InputIt额外满足RandomAccessIterator，复杂性是不变的。
例
二次
#include <iostream>
#include <iterator>
#include <vector>
int main()
{
std::vector<int> v{ 3, 1, 4 };
std::cout << "distance(first, last) = "
<< std::distance(v.begin(), v.end()) << '\n'
<< "distance(last, first) = "
<< std::distance(v.end(), v.begin()) << '\n';
}
二次
产出：
二次
distance(first, last) = 3
distance(last, first) = -3
二次
另见
| advance | advances an iterator by given distance (function) |
|---|
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