Macro definition ARRAY_SIZE

Question

I encountered the following macro definition when reading the globals.h in the Google V8 project.

// The expression ARRAY_SIZE(a) is a compile-time constant of t         


        

Answer 1

latter part will always evaluates to 1, which is of type size_t,

Ideally the later part will evaluate to bool (i.e. true/false) and using static_cast<>, it's converted to size_t.

why such promotion is necessary? What's the benefit of defining a macro in this way?

I don't know if this is ideal way to define a macro. However, one inspiration I find is in the comments: //You should only use ARRAY_SIZE on statically allocated arrays.

Suppose, if someone passes a pointer then it would fail for the struct (if it's greater than pointer size) data types.

struct S { int i,j,k,l };
S *p = new S[10];
ARRAY_SIZE(p); // compile time failure !

[Note: This technique may not show any error for int*, char* as said.]