Re: [Cygwin-ports-general] Ncview

[Michael Enright <mike@kmcardiff.com>]

On Thu, Oct 1, 2015 at 10:35 AM, Yaakov Selkowitz <yselkowitz@cygwin.com> wrote:
>
> Confirmed.  Often 64-bit-only issues come down to one or more of the
> following:
>
> * implicit function declarations.  Per the C standard, argument types
> are assumed to match whatever is given (which may be wrong if e.g. 0 is
> used instead of 0L or (PointerType)0 or NULL etc.) and the return type
> is assumed to be int (which will truncate the actual return value when
> it is actually a long/pointer).
>
> * vararg types.  Because these types aren't declared, the compiler can't
> automatically cast values to the correct type, so literal values and
> symbolic constants must be explicitly cast if they are not meant to be
> an int and are not obviously a long/pointer.
>

Good list. I would also add attempting to store pointer differences in
an "int" instead of ptrdiff_t and the issue you can see from
https://en.wikipedia.org/wiki/64-bit_computing#64-bit_data_models,
which is that the integer types other than long long on 64-bit Windows
are 32-bits while on 64-bit Linux 'long' and 'long long' are both
64-bit. This issue means that 'long' is a good-enough hack for
ptrdiff_t on 64-bit Linux but not 64-bit Windows. Does Cygwin differ
from Windows itself on this issue? Most 32-bit-designed code is
probably more sensitive to the pointer-difference aspect of this.

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