undefined | Better HN

0 pointsdavid-gpu1y ago0 comments

> Not really: C structs notably don't have variable-length fields

Feast your eyes: C99 introduced an ~~abomination~~ feature called flexible array members (FAM), which allows the last member of a struct to be a variable length array.

If you want to ~~gouge you eyes~~ learn more, see section 6.7.2.1.16 [0].

> To add insult to injury, it does not offer a standard way to determine field lengths

That's awful. You can sort of say the same about variable length struts in C, but at least the strict tupe definition usually has a field that tell you the length of the variable length array at the end.

[0] https://rgambord.github.io/c99-doc/sections/6/7/2/1/index.ht...

0 comments

lxgr1y ago

> [...] feature called flexible array members (FAM), which allows the last member of a struct to be a variable length array.

Oh, ISO 8583 has these too!

Sometimes they're even combined with the "feature" described in the article where there's a variable number of fixed-length elements, except for the last element, which is a variable-length string (or sometimes the last field type repeated n times). That's always "fun" to work with.

ISO 8583 really is a living museum of all ideas people had about binary encoding in the last half century or so.

j16sdiz1y ago

FAM was a (not so successful) attempt to standardise some existing usage

j / k navigate · click thread line to collapse