Is typeof in C, really an operator?
I'm thinking because there is no polymorphism in C, that there is nothing to do at run-time. That is, the answer to typeof is known at compile-time. (I can't think of a use of typeof that would not be known at compile time.) So it appears to be more of a compile-time directive, than an operator.
Does typeof use any (processor) run-time (in GCC)?
Since typeof is a compiler extension, there is not really a definition for it, but in the tradition of C it would be an operator, e.g sizeof and _Alignof are also seen as an operators.
And you are mistaken, C has dynamic types that are only determined at run time: variable modified (VM) types.
size_t n = strtoull(argv[1], 0, 0);
double A[n][n];
typeof(A) B;
can only be determined at run time.
Add on in 2024: typeof with similar rules as for sizeof made it into C23.
double with just missing boundaries sizes. Anyway, VLA's are not recommended as they generate lots of code and they are slow. ex: Linux removed all it;sIt's a GNU extension. In a nutshell it's a convenient way to declare an object having the same type as another. For example:
int x; /* Plain old int variable. */
typeof(x) y; /* Same type as x. Plain old int variable. */
It works entirely at compile-time and it's primarily used in macros. One famous example of macro relying on typeof is container_of.
It is a C extension from the GCC compiler , see this.
It's not exactly an operator, rather a keyword. And no, it doesn't do any runtime-magic.
One case in which you will need to use this extension is to get the pointer of an anonymous structs. You can check this this question for an example.
There is no function like that in c to determine, But you can use preprocessor + GCC feature
#define typeof(x) _Generic((x), \
int: "int", \
float: "float", \
double: "double", \
char: "char", \
default: "unknown")
And this is an example of how to use it
int x = 10;
printf("Typeof x: %s \n", typeof(x));
typeof() since the output of the _Generic() is a character string. You can do int a; char cc[] = typeof(a); however you can't do int a; typeof(a) b; since it doesn't return the type but rather a string indicating the type.
typeofoperator, that is a compiler extension.typeof. :)