iterate std::vector<std::vector<char> >?

Question

I have a vector like this:

std::vector<std::vector<char> > _lines;

I would like to iterate these vector and the vector contained within, however I'm not sure how I'd access the inside vector using the iterator of the first one?

I have the following already:

std::vector<std::vector<char> >::iterator first_iter = _lines.begin();

        for (; first_iter != _lines.end(); first_iter++)
        {
            (*first_iter)::iterator second_iter = (*first_iter)->begin();  // something is wrong with this? How do I get the second vector to iterate?
        }

Answer 1

for (std::vector<std::vector<char> >::iterator i = _lines.begin();
                                               i != _lines.end(); ++i)
{
    for (std::vector<char>::iterator j = i->begin(); j != i->end(); ++j)
    {
        // ... use *j
    }
}

If you use a modern compiler, you can use the C++0x feature auto to deduce the type automatically:

for (auto i = _lines.begin(); i != _lines.end(); ++i)
{
    for (auto j = i->begin(); j != i->end(); ++j)
    {
        // ... use *j
    }
}

Answer 2

You can't specify a type like this (*first_iter)::iterator . Just use std::vector<char>::iterator .

(*first_iter)->begin() should be (*first_iter).begin() (or first_iter->begin() ). *first_iter is a std::vector<char> , not a pointer.

Answer 3

您需要自己拼写内部迭代器的类型，而不能通过实例上的作用域运算符::访问类的类型。

std::vector<char>::iterator second_iter = ...

Answer 4

std::vector<std::vector<char> >::iterator first_iter =_lines.begin();
for (; first_iter != _lines.end(); first_iter++) {

     std::vector<char>::iterator second_iter = (*first_iter).begin(); // or first_iter->begin()
     ...
}

Answer 5

This would be the way to do it:

std::vector<std::vector<char> >::iterator first_iter = _lines.begin();

for (; first_iter != _lines.end(); first_iter++)
{
   std::vector<char>::iterator second_iter = first_iter->begin();
}