sizeof(int[1]) means what ?

hi, i'm reading the file ioctl.h, there i encountered a macro _IOC_TYPECHECK(t) which looks like: #define _IOC_TYPECHECK(t) \ ((sizeof(t) == sizeof(t[1]) && \ sizeof(t) < (1 << _IOC_SIZEBITS)) ? \ sizeof(t) : __invalid_size_argument_for_IOC) in this code ,what does sizeof(t[1]) mean? i mean the argument of this macro in a type(int, float), in that case what does sizeof(int[1]) specify? I have written a small test program which prints the value of the expression 4. Thank you