On 08/13/2017 05:41 AM, Toebs Douglass wrote:
Is it reasonable to assume a ptrdiff_t can be stored in a void * on the vast majority of platforms supported by GCC? Are there any known cases where ptrdiff_t isn't just a signed int, but actually is a special, magic type?
Searching GCC headers for the POINTER_SIZE and PTRDIFF_TYPE macros should help answer the question (but see below). I see just one special type that's not signed int, though I'm not sure I'd call it magic. The msp430 targets (config/msp430/msp430.h) conditionally defines PTRDIFF_TYPE to be __int20, but it also defines POINTER_SIZE to 20. That said, I don't know if the same size is necessarily a guarantee that an arbitrary ptrdiff_t value can be stored in a void* on all supported targets. C makes it possible for a target to trap when a bit pattern that doesn't correspond to a valid pointer value is stored in an object of pointer type. Martin
