operator - >不适用于自定义输入迭代器

Question

I have a complex data structure for which I want to define an input iterator. I want to avoid modifying the content through the iterator so operator* should return a const reference.

The problem is that when I try to use -> on the iterator with a const method I get an error:

base operand of -> has non-pointer type MyInputIterator

Here is a minimal example:

// this is supposed to be a much more complex data structure
std::vector<std::string> a = {"a", "b", "c", "d", "e"};

class MyInputIterator : std::iterator<std::input_iterator_tag, std::string>
{
public:
    MyInputIterator(int i = 0)
    {
        j = min(i, a.size());
    }

    MyInputIterator& operator++()
    {
        j = min(j + 1, a.size());
        return *this;
    }

    const std::string& operator*() const
    {
        return a[j];
    }

    ...

private:
    int j;
};

int main()
{
    MyInputIterator it(0);
    // error: base operand of '->' has non-pointer type 'MyInputIterator'
    std::cout << it->size() << std::endl;

    return 0;
}

Answer 1

You should add this to your iterator

const std::string* operator->() const
{
    return &a[j];
}

Now your main will work

Answer 2

In order to call operator->() on your MyInputIterator class you must first implement it.

In your case it would look something like:

const std::string* operator->() const 
{
    return &a[j];
}