What are type qualifiers in C++?

A type qualifier is a keyword that is applied to a type, resulting in a qualified type. For example, const int is a qualified type representing a constant integer, while int is the corresponding unqualified type, simply an integer. Type qualifiers are a way of expressing additional information about a value through the type system and ensuring correctness in the use of the data. As of 2014 and C11, there are four type qualifiers in standard C: const (C89), volatile (C89), restrict (C99) and _Atomic (C11). The first two of these, const and volatile, are also present in C++ and are the only type qualifiers in C++.