What is storage qualifiers in c?

Answer 1

A C++ qualifier is a keyword that contains semantic information related to a type. In other words, they are used to qualify a type.

The C++ qualifiers are const, mutable, restrict and volatile. Qualifiers do not alter the type's storage capacity nor how that storage is interpreted in any way.

The const qualifier is used to qualify that a type cannot be modified once it is initialised. As such, constants must be initialised at the point of instantiation, like so:

const int meaning_of_life = 42;

The const qualifier can also be used to qualify function arguments, like so:

void foo(const int x) { ... }

In this case, x is instantiated and initialised whenever the function is called.

The const qualifier can also be used with class instance methods (non-static member functions):

void foo::method() const { ... }

In this case, the const qualifier applies to the hidden this pointer, and thus ensures that the instance's non-mutable member attributes cannot be modified. Constant member methods may only access other other constant member methods of the same instance.

The mutable qualifier applies to class instance member data only. Data that is qualified as mutable may be modified by any method, including constant methods. You will typically use this feature for internal class data that does not alter the outward appearance of an object in any way. For instance, you might use internal caches or counters that do not alter the outward appearance of an object. If these members were not qualified as mutable, you wouldn't be able to modify them from within any constant methods. Note that the compiler uses a bitwise constant check to ensure all members remain unchanged within a constant method. The mutable keyword simply excludes the specified members from this check.

The restrict qualifier is not strictly a qualifier as it is not part of the C++ standard (it was introduced in C99) but some compilers support it. The restrict qualifier applies to pointers and references and merely provides a promise to the compiler that the object being referenced will only be access through the restricted reference or through copies of that reference.

The volatile qualifier denotes that a memory location may be modified by hardware or by external processes.

Answer 2

short, long, long long

signed, unsigned

const, volatile

Answer 3

static, extern, auto, register

(and typedef, but only formally)