[TUHS] Utility of C changes (Was: phototypesetter C)

I was thinking about this, with my memory of the changes refreshed by re-reading those 'changes to C' notes, and it's interested how many of them were ones I personally (and most of the people working with me) didn't use. Here is a list of the changes described in those 3 documents: 'newstuff': - Longs - Unsigneds - Blocks (locals declared inside a non-top-level {} pair) - Initialization of structures - Initialization of automatic variables - Bit fields - Macro functions - Macro conditionals (#ifdef) - Arguments in registers - Typedefs - 'Static' scope 'Changes': - Multi-line macros - Undefine - Conditional expressions (#if) - Unions - Casts - Sizeof() on abstractions - '=' in initializations - Change binary operators from trailing to leading - 'extern' does not allocate storage (This note also includes unsigneds, blocks, and structure initializations, from the earlier? note.) 'cchanges': - Structure assignment and argument/return-value - Enum Of these, I never really used quite a few: blocks, automatic initializations, typedefs, unions, structure assignment/etc, or enum. I'm not sure if I ever used bit fields, either. Some of these are understandable; e.g. automatic initializations are just syntactic sugar (as are register arguments, but I did use those). Typedef is also effectively syntactic sugar; you can always use a macro and get almost (entirely?) the same result. In fact, I devised an entire system of types to make the code I was working on (almost entirely networking code, so lots of packet headers from other machines, etc) more rigorous - and later it turned out it had made it much more portable; it all used macros, not typedef. I don't think I ever used typedef... (The details of that might be of some interest: instead of int, long, etc we had things of the form {type}{len}, where {type}pe} was 'int', 'uns', 'bit', etc and length was 'b', 's', 'l', or two other interesting ones 'w' and 'f' - 'w' meant the machine's native word length, and 'f' meant whatever was fastest on the machine. So 'unsl' mean '32-bit unsigned'. Depending on the machine, the compiler couldn't always produce them all - e.g. the PDP-11 didn't have unsl - so sometimes you had to live with non-optimal replacements. There were also un-typed types, i.e. 'byte', 'swrd', 'lwrd' - 8, 16 and 32 bits - and 'word' - the machine's native length.) Unions didn't get used much either, in our stuff, although one would think it would be useful in network code - you get a packet with a pile of bits inside it, which can be one of N different formats, seems like a perfect application for a union. The problemis that it tied two different subsystems intimately together. If you have protocol A and protocol B, if you use a union to define the header format, the union has to have both A and B in it. Now if you want to add protocol C, that requires modifying that union definition. It was much easier to just take a pointer to the outer packet's data area, and assign (with cast) it to a new pointer variable which was of the correct type for the header you were trying to process. Some of the new things were incredibly useful, though - or, in fact, one couldn't get by without them. Casts were incredibly useful once the compiler got pickier. Initialization of structures was huge - other than 'bdevsw'-like hacks, there was just no other way to do that. Noel