vector<int>::size_type in C++

Question

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 .

Answer 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 .

Answer 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.

Answer 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.

Answer 4

Different implementations use different types to represent sizes, so we cannot write the appropriate type directly and remain implementation-independent. For that reason, it is good programming practice to use the size_type that the library defines to represent container sizes.

- Accelerated C++ by Andrew Koenig and Barbara E. Moo