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auto is mostly useful when tinkering with type-generic macros, but shouldn't be used in regular code (e.g. please no 'almost always auto' madness like it was po

auto is mostly useful when tinkering with type-generic macros, but shouldn't be used in regular code (e.g. please no 'almost always auto' madness like it was popular in the C++ world for a little while). Unfortunately there are also slight differences between compilers (IIRC Clang implements a C++ style auto, while GCC implements a C style auto, which has subtle differences for 'auto pointers' - not sure if those differences have been fixed in the meantime). _BitInt(N) isn't typically used directly but typedef'ed to the width you need, e.g. typedef _BitInt(2) u2; The 'ugly' _B syntax is needed because the combination of underscore followed by a capital letter is reserved in the C standard to avoid collisions with existing code for every little thing added to the language (same reason why it was called _Bool). AFAIK defer didn't actually make it into C23? I'm also more on the conservative side when it comes to adding features to the C standard, but IMHO each of the C23 additions makes sense.

humanrebar 2y ago
> IIRC Clang implements a C++ style auto, while GCC implements a C style auto, which has subtle differences for 'auto pointers' - not sure if those differences have been fixed in the meantime Both have compatibly implemented the standard C++ auto. Since 2011 or so.
- flohofwoe 2y ago
  Well, not in C :) Here's an example where Clang and GCC don't agree about the behaviour of auto in C23: https://www.godbolt.org/z/WchMK18vx https://www.godbolt.org/z/WchMK18vx IIRC Clang implements 'C++ semantics' for C23 auto, while GCC doesn't. Last time I brought that up it turned out that both behaviours are 'standard compliant', because the C23 standard explicitly allows such differing behaviour (it basically standardized the status quo even if different compilers disagreed about auto semantics in C). PS: at least Clang has a warning now in pedantic mode: https://www.godbolt.org/z/ovj5r4axn https://www.godbolt.org/z/ovj5r4axn
  - johnisgood 2y ago
    This difference of implementation in two of the major C compilers leaves a bad taste in my mouth. :/
  - cpeterso 2y ago
    > PS: at least Clang has a warning now in pedantic mode: https://www.godbolt.org/z/ovj5r4axn https://www.godbolt.org/z/ovj5r4axn Did you mean gcc? Your link shows a gcc error: <source>:3:5: error: 'auto' requires a plain identifier, possibly with attributes, as declarator 3 | auto* p = &i; | ^~~~
    - flohofwoe 2y ago
      No, GCC is right to error there, because the code uses a C++-ism (the '*' after 'auto' only makes sense in C++ but not in C).
eqvinox 2y ago
> AFAIK defer didn't actually make it into C23? Correct, defer didn't make it into C23. It (in its __attribute__((cleanup())) form) is also one of the most useful extensions in GCC/clang — but, again, for use in macros.

humanrebar 2y ago

> IIRC Clang implements a C++ style auto, while GCC implements a C style auto, which has subtle differences for 'auto pointers' - not sure if those differences have been fixed in the meantime Both have compatibly implemented the standard C++ auto. Since 2011 or so.

flohofwoe 2y ago
Well, not in C :) Here's an example where Clang and GCC don't agree about the behaviour of auto in C23: https://www.godbolt.org/z/WchMK18vx https://www.godbolt.org/z/WchMK18vx IIRC Clang implements 'C++ semantics' for C23 auto, while GCC doesn't. Last time I brought that up it turned out that both behaviours are 'standard compliant', because the C23 standard explicitly allows such differing behaviour (it basically standardized the status quo even if different compilers disagreed about auto semantics in C). PS: at least Clang has a warning now in pedantic mode: https://www.godbolt.org/z/ovj5r4axn https://www.godbolt.org/z/ovj5r4axn
- johnisgood 2y ago
  This difference of implementation in two of the major C compilers leaves a bad taste in my mouth. :/
- cpeterso 2y ago
  > PS: at least Clang has a warning now in pedantic mode: https://www.godbolt.org/z/ovj5r4axn https://www.godbolt.org/z/ovj5r4axn Did you mean gcc? Your link shows a gcc error: <source>:3:5: error: 'auto' requires a plain identifier, possibly with attributes, as declarator 3 | auto* p = &i; | ^~~~
  - flohofwoe 2y ago
    No, GCC is right to error there, because the code uses a C++-ism (the '*' after 'auto' only makes sense in C++ but not in C).

eqvinox 2y ago

> AFAIK defer didn't actually make it into C23? Correct, defer didn't make it into C23. It (in its __attribute__((cleanup())) form) is also one of the most useful extensions in GCC/clang — but, again, for use in macros.