Chris Angelico <ros...@gmail.com> Wrote in message: > On Sun, Mar 2, 2014 at 3:02 PM, Dave Angel <da...@davea.name> wrote: >> The quote you make from the C standard doesn't mention malloc, so >> you're arguing different things. It's not the compiler that casts >> the malloc return value to the struct type. >> >> C++ does implicitly convert the result, and the return value of >> new already has the struct type. But the runtime stores at least >> two kinds of overhead on occasion, the array size, and the >> vtable. So the malloc address can not be assumed to match the >> struct beginning. (Not even considering that one can override > > Whatever pointer malloc returns is the beginning of the *usable* > space. Any overhead for array size etc has to be before that; a > virtual function table pointer would be inside that space, but that's > very much compiler-dependent. >
Sure, for some definition of "usable". Overhead such as block size, freelist pointer etc., are obviously outside of the returned block. But the array size that's specified in a call to new [], and the vptr, are definitely inside the malloc'ed block, and may be before the struct data. -- DaveA -- https://mail.python.org/mailman/listinfo/python-list
