Ken Raeburn <[EMAIL PROTECTED]> writes: > On Jul 9, 2008, at 12:55, Kjetil S. Matheussen wrote: >> On Wed, 9 Jul 2008, Greg Troxel wrote: >>> Does C guarantee that pointers fit in unsigned long? >> I don't know. But in practice: Yes. > > According to various sources, 64-bit Windows uses an LLP64 model -- > meaning long is 32 bits, long long and pointers are 64 bits. So, no.
I believe this is correct. I have been the 64-bit portability weenie on a large project at work, and been railing against int/* assignment. The overwhelming consensus among those of us that have actually dealt with making programs run on non-ILP32 machines is that int/* assignments are just plain wrong. > Near as I can tell, C99 does not require that there be *any* integral > type large enough to hold a pointer value (6.3.2.3 paragraph 6); and > specifically, uintptr_t and intptr_t are optional types. However, I > expect any C99 implementation we're likely to run across will have > such a type, and will define [u]intptr_t. I don't have a copy of the > C89 spec handy, though, and unfortunately that's where most compilers > are these days. My recent experience is that decent compilers are now essentially C99, and that Microsoft compilers are mostly C99 with a a few defects. Our strategy has been to patch around the defective compilers by defining the things we need somewhat like: #if defined(LOSING_COMPILER_A) #ifdef i386 typedef unsigned lont uintptr_t; #else #error DEFINE uintptr_t for yoru platfrom #endif #endif and then just rely on the C99 definition. Surprising little fixup has been needed. > In practice, it's also probably safe to use unsigned long long (or > whatever Windows calls it) on the platforms that have it, and unsigned > long on those that don't. But testing compiler properties in autoconf > and then using them in your installed headers may tie you to a > particular compiler when more than one may be available (e.g., > vendor's compiler and gcc). If we have to store a pointer we should just use void *. I see Ken's point about testing, but that quickly leads to madness as he notes.
