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

The second part wants to ensure that the sizeof( a ) is divisible of by sizeof( *a ).

Thus the (sizeof(a) % sizeof(*(a))) part. If it's divisible, the expression will be evaluated to 0. Here comes the ! part - !(0) will give true. That's why the cast is needed. Actually, this does not affect the calculation of the size, just adds compile time check.

As it's compile time, in case that (sizeof(a) % sizeof(*(a))) is not 0, you'll have a compile-time error for 0 division.