6 ms·

I wish folks would be wary of saying "such and such is legal in C _because an implementation accepts it_". I'm well aware that the practice is for compilers to

by jepler 3y ago

I wish folks would be wary of saying "such and such is legal in C _because an implementation accepts it_". I'm well aware that the practice is for compilers to accept this; it was a standard "feature" of K&R C. However, per Wikipedia, this feature was removed in C99 <https://en.wikipedia.org/wiki/ANSI_C#C99 https://en.wikipedia.org/wiki/ANSI_C#C99> a fact that I verified by reading the forward to the C99 draft standard ISO/IEC 9899:TC3. So I'm a little surprised that the construct is only treated with a warning in `gcc -std=c99 -ansi -pedantic -Wall`.

parasti 3y ago
-ansi translates to -std=c90, so you're effectively cancelling the -std=c99.
xorvoid 3y ago
There must be other context to the tweet because I’m sure that Walter Bright knows all of that..
- n4r9 3y ago
  To be fair, the linked Tweet does not claim it is legal behaviour. Just that it ought to be possible, in principle, in at least some situations.
  - classified 3y ago
    Just declare fwd() with a prototype, and everything's good.
pjmlp 3y ago
First they need to learn to distinguish what is ISO C and whateve their compiler accepts, the large majority doesn't. Hence why so many just try to use GCC everywhere (nowadays clang as well).
eqvinox 3y ago
> So I'm a little surprised that the construct is only treated with a warning GCC does that for everything short of actual things it can't compile, you have to use -Werror[=…] to make it error out.
gpderetta 3y ago
Recently GCC moved to make this an hard error by default in >=C99 mode. There was huge push back form some very vocal members of the community against such exoteric, bleeding edge type system non-sense like function prototypes; according to them having to add -pedantic to the gcc command-line to build legacy code is an unreasonable breaking change. The burden should be on beginners to find the correct GCC arguments to enable all the "useless" warning. Thankfully GCC is going ahead with the change anyway.
unwind 3y ago
Yeah, perhaps even more when they wrote said implementation. :) Nothing against WalterBright, I just thought it was funny to use your own compiler as a referene like that. I don't quite understand the point, is forward references to undeclared things something to strive after?
- MathMonkeyMan 3y ago
  It prevents you from having to topologically sort your definitions, or otherwise declare everything at the top. Since idiomatic C uses header files, though, it doesn't matter too much. Main benefit is that non-public implementation details (e.g. static functions) needn't be declared at the top of the source file.
taneq 3y ago
There’s no such language as C anyway, strictly speaking. There’s the C standard which defines a family of languages, then there’s the (C compiler version, OS, misc factors) tuples that define actual C-like languages.
- kyberias 3y ago
  What is ANSI C or C99 then?
  - MathMonkeyMan 3y ago
    According to the parent post, two families of languages. I disagree, though. Each standard _is_ a language. But which one does your compiler implement?
    - taneq 3y ago
      Exactly, it's "a language" but what you say will be interpreted differently depending on which specific version of which specific compiler you happen to be using today.
jmclnx 3y ago
I not think you know who Walter Bright is :) In my opinion he wrote wrote of the best c/c++ compilers for DOS. If he says something compiler (c) related, I usually pay attention.

by jepler 3y ago

parasti 3y ago

-ansi translates to -std=c90, so you're effectively cancelling the -std=c99.

xorvoid 3y ago

There must be other context to the tweet because I’m sure that Walter Bright knows all of that..

n4r9 3y ago
To be fair, the linked Tweet does not claim it is legal behaviour. Just that it ought to be possible, in principle, in at least some situations.
- classified 3y ago
  Just declare fwd() with a prototype, and everything's good.

pjmlp 3y ago

First they need to learn to distinguish what is ISO C and whateve their compiler accepts, the large majority doesn't. Hence why so many just try to use GCC everywhere (nowadays clang as well).

eqvinox 3y ago

> So I'm a little surprised that the construct is only treated with a warning GCC does that for everything short of actual things it can't compile, you have to use -Werror[=…] to make it error out.

gpderetta 3y ago

Recently GCC moved to make this an hard error by default in >=C99 mode. There was huge push back form some very vocal members of the community against such exoteric, bleeding edge type system non-sense like function prototypes; according to them having to add -pedantic to the gcc command-line to build legacy code is an unreasonable breaking change. The burden should be on beginners to find the correct GCC arguments to enable all the "useless" warning. Thankfully GCC is going ahead with the change anyway.

unwind 3y ago

Yeah, perhaps even more when they wrote said implementation. :) Nothing against WalterBright, I just thought it was funny to use your own compiler as a referene like that. I don't quite understand the point, is forward references to undeclared things something to strive after?

MathMonkeyMan 3y ago
It prevents you from having to topologically sort your definitions, or otherwise declare everything at the top. Since idiomatic C uses header files, though, it doesn't matter too much. Main benefit is that non-public implementation details (e.g. static functions) needn't be declared at the top of the source file.

taneq 3y ago

There’s no such language as C anyway, strictly speaking. There’s the C standard which defines a family of languages, then there’s the (C compiler version, OS, misc factors) tuples that define actual C-like languages.

kyberias 3y ago
What is ANSI C or C99 then?
- MathMonkeyMan 3y ago
  According to the parent post, two families of languages. I disagree, though. Each standard _is_ a language. But which one does your compiler implement?
  - taneq 3y ago
    Exactly, it's "a language" but what you say will be interpreted differently depending on which specific version of which specific compiler you happen to be using today.

jmclnx 3y ago

I not think you know who Walter Bright is :) In my opinion he wrote wrote of the best c/c++ compilers for DOS. If he says something compiler (c) related, I usually pay attention.