如何使用 std::istreambuf_iterator 初始化字符串

Question

So I'm trying to read a piece of code which goes

auto runFile(const std::string &path)
{
    const std::string source = ([&]() {
        std::ifstream file(path);
        return std::string{std::istreambuf_iterator<char>{file}, std::istreambuf_iterator<char>{}};
    })();
}

Could someone explain to me exactly what's happening in this line:

return std::string{std::istreambuf_iterator<char>{file}, std::istreambuf_iterator<char>{}};

I understand that it's supposed to return a string that is made up of a range between the two iterators, but i don't exactly understand what range is being selected here.

If someone could explain to me how istreambuf works in the first place that would be great too!

The simpler an answer the better, as I'm new to c++

Answer 1

The default-constructed std::istreambuf_iterator is known as the end-of-stream iterator.

In other words, the first iterator being passed points to a valid stream and the second iterator being passed, which is default constructed, represents the end of the stream .

cppreference

When a valid std::istreambuf_iterator reaches the end of the underlying stream, it becomes equal to the end-of-stream iterator. Dereferencing or incrementing it further invokes undefined behavior.