C++ 带 {} 的空迭代器

Question

I found this answer on stack overflow for reading a stream into a string . The code std::string s(std::istreambuf_iterator<char>(stream), {}); works just fine for what I was doing, but I was really confused about the {} . As far as I can tell this is using the std::string constructor that uses a begin and end iterator, but I've never seen an iterator defined with {} . What does that mean and how is it achieving the same thing as std::istreambuf_iterator<char> eos; ?

Answer 1

{} is a braced initialiser list in this context. It is a list of initialisers used to initialise an object. It is used to initialise a temporary object.

In this case, the list of initialisers is empty. In such case, the object will be value initialised. In case of a non-trivially-default-constructible class such as std::istreambuf_iterator value initialisation means that the default constructor will be used.

A default consturcted std::istreambuf_iterator is a sentinel that represents end of stream. This is a feature specific to stream iterators and not to all other iterators.