C ++-迭代器向量的迭代器未编译

Question

I have a templated class P that has a const_iterator and i'm trying to make a vector of said iterators and iterate through that vector:

std::vector<typename P<A, B>::const_iterator>::const_iterator it;

problem is when i try to compile i get

error: expected ‘;’ before ‘it’

any ideas as to why this is happening?

Answer 1

你需要一个typename之前std::vector<>以及因为在模板参数中的至少一个P<A, B>是一个依赖型：

typename std::vector<typename P<A, B>::const_iterator>::const_iterator it;

Answer 2

Both uses of const_iterator depend on template parameters; so both need typename .

typename std::vector<typename P<A, B>::const_iterator>::const_iterator it;
^^^^^^^^             ^^^^^^^^