Question

In C++, as far as I know, all data types are implemented as classes. ( Don’t know if it is right, but I read it as a justification for statements such as int a(5); which calls the parametric constructor of int. )

If so, how are long and short implemented? I just found out that long long and short short are valid types but short long and long short are not (Checked the latter ones just because it sounds funny!)

Similarly, how are signed and unsigned implemented?

PS. By implemented, what I mean is “Is written using C/C++ features or is it written at a lower level in the compiler itself”.

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So the equivalent parts of declaration of variable of a basic type and a userdefined object or variable is (read downwards)

auto|register|static|extern           <=>   auto|register|static|extern
const                                 <=>   const
(signed|unsigned)(long|short)datatype <=>   class name etc
variable name                         <=>   object/variable name

? Is that assusmption correct?

Answer 1

On the particular question, long long is implemented by the compiler in a compiler + platform specific way (usually more platform than compiler dependent).

As to the original misconception, no, not all types are classes in C++. The languages tries to provide a uniform syntax in as much as possible for all types, trying to have all types behave similarly in as much as possible, and be used in a similar way. As a matter of fact, it is actually quite the other way around: C++ tries in as much as possible to have classes behave like primitive types (value semantics).

The particular reason to be able to initialize an integer that way is actually quite related to classes, just in a different way. In a class constructor definition there are initializer lists that define how each one of the members is initialized before the constructor block is executed. The syntax for each initializer element in the list is basically (I would have to lookup the exact definition): member_name( initializer ), so for example you would get:

class my_int_vector {
   int * p;
   int size; 
public:
   my_int_vector() : p(0), size(0) {}
//...
}

Both pointers and integers are fundamental types, but they can be initialized in a way similar to that of classes. If that type of initialization was not allowed for fundamental types, and only the type name = value; syntax was allowed, the initializer list syntax would have to be extended, and you would not be able to seamlessly change those types at a later time (say, change the int to a atomic_int).