问题
What is meant by this C++ statement?
vector<int>::size_type x;
And, what is the use of the scope operator :: here? In other words, how do we read this statement in English?
For example, for X::x(){...}, we say that x() is a member function of class X.
回答1:
size_type is a (static) member type of the type vector<int>. Usually, it is a typedef for std::size_t, which itself is usually a typedef for unsigned int or unsigned long long.
回答2:
I would read it as "declare x as a variable of a type suitable for holding the size of a vector". The vector defines its own type for its length, and it's always cleanest to use that if possible, rather than "guessing" and using int, unsigned int, long, unsigned long or size_t etc directly as you'd otherwise need to do.
回答3:
vector is a template
so the vector type templated with int has a member typedef called size_type. x is defined as a variable of that type.
来源：https://stackoverflow.com/questions/4849632/vectorintsize-type-in-c