Mark Dilger <[email protected]> writes:
> The mechanism that occurs to me (and I'm not wedded to
> this idea) is:
> typedef uint8 T_HOFF_TYPE;
> typedef struct xl_heap_header
> {
> uint16 t_infomask2;
> uint16 t_infomask;
> T_HOFF_TYPE t_hoff;
> } xl_heap_header;
> #define SizeOfHeapHeader (offsetof(xl_heap_header, t_hoff) +
> sizeof(T_HOFF_TYPE))
Meh. That does nothing for the "add a field in the wrong place" risk.
Yes, it would prevent people from changing the type of t_hoff without
updating the macro --- but I'm not convinced that defending against that
alone is worth any notational pain. If you're changing t_hoff's type
without looking fairly closely at every reference to t_hoff, you're
practicing unsafe programming to begin with.
I wonder though if we could invent a macro that produces the sizeof
a struct field, and then use that in macros like this. Something like
#define field_sizeof(typename, fieldname) \
sizeof(((typename *) NULL)->fieldname)
Compare the default definition of offsetof ...
regards, tom lane
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