🚀 go-pugleaf

From: thads@csn.net (Thad Smith)

> In article <41o4n4$m0l@newsbf02.news.aol.com>,
> ffarance@aol.com (FFarance) wrote:
> 
>  >> At present long is known to be the largest signed type, so I can
>  >> safely do the following:
>  >> 
>  >> ptrdiff_t x = 0;
>  >> printf("%ld", (long) x);
>  >> 
>  >> (where ptrdiff_t can be replaced by any typedef which I know to be
>  >signed & 
>  >> integral but don't know the exact type of). This is a very useful
> idiom,
>  >> and this cannot be done at all if there is no largest type.
>  >
>  > Unfortunately, this idiom isn't portable.  There is no guarantee
>  > that "ptrdiff_t" will fit in a "long", e.g., systems with 48-bit
>  > pointers and 32-bit "long" (some memory models in OS/2).  Another
>  > example is "fpos_t": it may be larger than "long".
> 
> In Standard C ptrdiff_t must be a signed integral type defined in
> Standard C (see enumeration of signed integer types in ANSI 3.1.2.5).
> There is no integral type in C larger than long int, hence casting to
> long should be portable.  Note, however, that overflow is possible as
> a result of subtracting pointers.  fpos_t can certainly be larger than
> a long -- it isn't even restricted to be a scalar type, let alone
> arithmetic or integral, but might be a structure.

Boy my head must have been screwed on wrong that day (-:!  You're right
on both points.  The first point on "long" being the longest type is
true for strictly conforming applications (which was your point).  I was
thinking of the extended integer work were I think many assume "long"
won't
remain the longest type in C9X.  I'll include your example in the SBEIR
proposal as an issue.

In my multiplication example, I was assuming that "fpos_t" was an
integral type for that implementation.  The point was to generate a
temporary with enough precision - I'll use a better example.

Thanx for pointing out my mistakes.

-FF
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(``I only use AOL for reading netnews.'')
Frank Farance, Farance Inc.
E-mail: frank@farance.com, Telephone: +1 212 486 4700
ISO JTC1/SC22/WG14 & ANSI X3J11 (C Programming Language) Project Editor