11.6 Type Designators

Some C constructs require a way to designate a specific data type independent of any particular variable or expression which has that type. The way to do this is with a type designator. The constructs that need one include casts (see Explicit Type Conversion) and sizeof (see Type Size).

We also use type designators to talk about the type of a value in C, so you will see many type designators in this manual. When we say, “The value has type int,” int is a type designator.

To make the designator for any type, imagine a variable declaration for a variable of that type and delete the variable name and the final semicolon.

For example, to designate the type of full-word integers, we start with the declaration for a variable foo with that type, which is this:

int foo;

Then we delete the variable name foo and the semicolon, leaving int—exactly the keyword used in such a declaration. Therefore, the type designator for this type is int.

What about long unsigned integers? From the declaration

unsigned long int foo;

we determine that the designator is unsigned long int.

Following this procedure, the designator for any primitive type is simply the set of keywords which specifies that type in a declaration. The same is true for compound types such as structures, unions, and enumerations.

Designators for pointer types do follow the rule of deleting the variable name and semicolon, but the result is not so simple. See Pointer-Type Designators, as part of the chapter about pointers. See Array Type Designators), for designators for array types.

To understand what type a designator stands for, imagine a variable name inserted into the right place in the designator to make a valid declaration. What type would that variable be declared as? That is the type the designator designates.