cswiger at mac.com
Wed Aug 17 21:45:58 GMT 2005
Sergey Matveychuk wrote:
> I know it may be stupid, but I can't understand this sentence from
> malloc(3) man page:
> The allocated space is suitably aligned (after possible pointer
> coercion) for storage of any type of object.
> What does "suitable aligned for storage of *any* type of object" means?
On some platforms, it is either desirable or required that, say, a 8-byte
double is stored at a memory location which is is also aligned to 8-bytes:
0x1000 for example, rather than any of (0x1001, 0x1002, 0x1003, ... 0x1007)
> What is pointer coercion? I have no pointer before malloc() returns.
Right. Well, malloc returns a (void *), but most people want to use the memory
malloc returns to hold their own arrays, structs, whatever, which means that
you need to be able to coerce the (void *) malloc gave you into whatever
pointer type you want to actually use.
So the memory malloc gives you needs to be aligned so that it's OK to be used
for even the most restrictive datatype known to the system, commonly 8, 16, or
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