Richard Hartman wrote:
> Yes, it is all transparent to you -unless- you
> start trying to calculate offets from a void *,
> in which case you must be aware of the padding
> issues.
To calculate struct member offsets, use the offsetof macro:
#define offsetof(type, member) \
((unsigned int) &(((type *) 0)->member))
This macro in in <stddef.h> in the Metrowerks library; just paste it
into a convenient header for use in a Palm project.
This macro will always return the correct offset value, such as for
using DmWrite to write a single field of a struct located in storage
memory. It forces the compiler to do all the math including accounting
for any padding in the struct. Very handy.
Basically my rule is: if you find yourself doing any math yourself to
figure out sizes or offsets, then you're probably doing something wrong
and should look for a way to make the compiler do the work. That's what
sizeof and offsetof (and countof, for arrays) are for.
-slj-
