Author: Carey
Date: 13:58:01 09/05/05
Go up one level in this thread
On September 05, 2005 at 14:44:58, Robert Hyatt wrote: > > void *p = (void *) ((int) malloc(size+63) + 63) & ~63); > >What I do is malloc 63 bytes more than I need, add 63 to the resulting pointer, >then and with a constant (an int unfortunately) that has the rightmost 6 bits I always did that seperately. Allocate it and then cast to unsigned int, and then masked off how much I needed, then added that to the original pointer. That way the pointer never had a chance to be truncated. That was back in the days of 16 bit near vs. far pointers in DOS, but the same thing works with 64 bit systems. A couple of macros can easily hide the nastiness of all the type casts etc. that keep the compiler happy. >32 bits, pointer (and long) = 64 bits... Why an int is 32 bits on a 64 bit >machine is a good question. We really needed some better int types, but the Up to the compiler designer. Realistically, it makes quite a bit of sense. So much code today is hardwired for 32 bit ints that going fully 64 by default would cause a lot of code to fail. By keeping the int at 32 bits, most semi-properly written code will still compile and work. It'd be nice if all the code was properly written, but it's not. >ANSI C committee failed to deliver them. int16, int32, int64 would have been a We have that. That's what the stdint.h header does. It was added in C99. It isn't in the C89 standard because at the time, they were concentrating on "codifying existing practice". In other words, just figuring out what all the existing k&r compilers were already doing, and how to clean up the murky areas. That alone was a major effort. Unfortunately, it's not in C++, so that can screw up portability and linking both C and C++ together. Not only does it define those things, it also allows 'at least' that size, and 'fast' sized integers, etc. So the machinery is there. We just needed better tools to access them. For code that has to be portable, it's just a matter of the preprocessor checking what version you have, including stdint if it's c99, and if not, then just typedefing some reasonable defaults. And then never using the plain 'int' but using known sized integers. Personally, I've always missed the somewhat stronger type checking of Pascal. (Not the full ISO typechecking, but a little better than what C has.) A little bit better type checking can be a major help.
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