"Earl Purple" <[EMAIL PROTECTED]> writes:
> So I receive the binary representation for a double (500000 in this
> particular case, which is 0x41 0x1e 0x84 0x80 0x00 0x00 0x00 0x00)
>
> If I reinterpret_cast the pointer to const double * then dereference it
> I get a Bus Error (core dumped).
The buffer into which you received the data must not have been
properly aligned.
> The workaround (that works) is to copy the buffer into a double, i.e.
> take a double, reinterpret_cast its address to unsigned char * and copy
> the buffer. That works, no crash.
You have to either do that, or ensure that the data is properly
aligned in the buffer. For example:
char buf[200];
receive_data(buf, sizeof(buf));
double *p = reinterpret_cast<double*>(buf); // BAD
double d = *p; // SIGBUS
do this instead:
union { char buf[200]; double d; } u;
receive_data(u.buf, sizeof(buf));
double *p = reinterpret_cast<double*>(u.buf); // OK
p = &u.d; // same thing
> It worked fine until I compiled in release mode with O3 optimisation
> setting.
So gcc decided to pack things differently on the stack, and your
buffer shifted its alignment. What else is new?
> Is this a known bug
Yes, in your program ...
> (as far as I'm aware it is not undefined behaviour)?
I am sure it *is*, but am too lazy to find the exact wording.
Cheers,
--
In order to understand recursion you must first understand recursion.
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