为什么std :: distance不工作在const和nonconst迭代器的混合？ [英] Why std::distance doesnt work on mix of const and nonconst iterators?

问题描述

像问题所说，我想知道原因。因为当我尝试获取 const 和非 - const 迭代器之间的距离时，我得到一个错误。

Like the question says, I'm wondering about the reason for that. Because I get an error when I try to get the distance between const and non-const iterators.

vector<int> v;
auto it=v.begin();
auto cit=v.cbegin();
distance(it,cit);


no matching function for call to ‘distance(__gnu_cxx::__normal_iterator<int*, std::vector<int> >&, __gnu_cxx::__normal_iterator<const int*, std::vector<int> >&)

从我对迭代器的有限理解，没有理由为什么它不应该工作。

From my limited understanding of iterators, I see no reason why it shouldn't work.

推荐答案

在调用 std :: distance

You have a mutable iterator and a constant iterator in the call to std::distance, so template argument deduction is failing. You can fix this by specifying the template argument explicitly.

std::vector<int> v;
auto i1 = v.begin();
auto i2 = v.cbegin();

auto dist = std::distance<std::vector<int>::const_iterator>( i1, i2 );

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