[OT] Can global variable be passed into Python function?
davea at davea.name
Sun Mar 2 14:22:57 CET 2014
Chris Angelico <rosuav at gmail.com> Wrote in message:
> On Sun, Mar 2, 2014 at 3:02 PM, Dave Angel <davea at 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.
More information about the Python-list