7 ms·

I think I have the opposite opinion. Newer C standards have a very high degree of backwards compatibility. I think we should try to transition code to the cur

by uecker 3y ago

I think I have the opposite opinion. Newer C standards have a very high degree of backwards compatibility. I think we should try to transition code to the current ISO standard and in almost all cases this will just work without problems. In the few cases, where it does not, it is usually for a very good reason. Now, nobody is stopping compilers from supporting old language modes, but it adds a lot of complexity, not for making the code compile, but for all the diagnostics which are different. If you look at the FE code of GCC, for example, a lot of code is dedicated this. If we could remove all this stuff at some point (which would still allow old code to compile, but one code remove diagnostics for things which were disallowed in earlier standards but are now allowed), then this reduce maintenance burden substantially. And if one really needs those old diagnostics, one could simply go back to an old version of the compiler.

sgbeal 3y ago
> I think we should try to transition code to the current ISO standard and in almost all cases this will just work without problems. In the few cases, where it does not, it is usually for a very good reason. Microsoft's C compiler did not support C99 until something like 15 years after the standard came out (and reportedly (according to colleagues who use that platform) still doesn't support certain features of it). It happens with surprising frequency that someone reports to the sqlite project that The Latest Version no longer works on their pre-2005 environment and they'd like to see it patched to work there. My point is: users of a given platform might not be able to use The Latest Stuff (or anywhere near it, for that matter) because their OS vendor is reticent, because they have to support an old platform which is not targeted by newer tools, or for whatever other reason. > Now, nobody is stopping compilers from supporting old language modes, but it adds a lot of complexity, ... i don't doubt that, and i do sympathize with the maintainers. i'm not saying they should never ever remove C89 support, but if they do then there needs to be an alternative, like a fork of the last compiler version which supported it, maintained at least to the extent that the rare genuine compiler bugs can be resolved.
- uecker 3y ago
  Microsoft declared C dead and wanted that everybody transitions to C++. Luckily this changed a bit and MSVC now supports newer standards. Also there are now other alternatives on Windows. So I do not think there is a good reason to put everything on standstill anymore. C needs to evolve and old code must be maintained. For me, this this means that code should be transitioned to newer standards. In no other industry would it be acceptable to ignore current industry standards. Now, I do understand that some projects do not want to use newer features for portability reasons. But this does not mean that they couldn't be compatible with a newer ISO C modes as well. Being compliant with C 17 does not necessarily mean one has to use new features.
- pjmlp 3y ago
  Microsoft considered C done, as clarified by Herb Sutter. https://herbsutter.com/2012/05/03/reader-qa-what-about-vc-and-c99/ https://herbsutter.com/2012/05/03/reader-qa-what-about-vc-an... They only kept updating their C support to the extent required by ISO C++ requirements, and some key customers. Anyone else still dependent on C was suggested to use clang, this is also why clang is part of Visual Studio compiler suite nowadays. Around the time the Microsoft <3 Linux stuff started, they decided to backtrack on this matter, and started updating their C support, however since C11 made a couple of stuff from C99 optional, they decided to skip on those. VLAs have anyway been proven a rich source of exploits, to the extent Google has sponsored the work to clean up the Linux kernel from all uses of them. https://www.phoronix.com/news/Linux-Kills-The-VLA https://www.phoronix.com/news/Linux-Kills-The-VLA
  - uecker 3y ago
    The VLA security problems are a bit of a myth. In the kernel it may be some problem, but with stack clash protection (which one should activate anyway) there isn't really a inherent security issue anymore. The code quality improvements of using VLAs usually make it worth using them IMHO.
    - pjmlp 3y ago
      A myth that was worth every penny fixing it, as per Google.
flohofwoe 3y ago
I would rather just announce to the compiler what standard version a given piece of code should adhere to (and it's fine if -std=2x doesn't accept older C standards except for header declarations - while at it, please remove the 'inline' keyword from the next C standard ;)) To some extent that's already possible with the "-std=..." option of course, but it would be better to also allow changing the standard version within the same compilation unit (at least if it turns out that including headers written in old C standards can't be supported, in that case I would like to wrap a block of #includes with a 'use c89 { ... }'). Random example for why it is important to allow older C versions to compile: I just made a mid-90's assembler for 8-bit CPUs written in C89 work in VSCode via WASM/WASI without requiring any code changes (and yes I've been looking long and hard for an alternative assembler tool which provides the same feature set written more recently without luck, I even considered writing my own assembler from scratch). It would suck if I had to port the code base to a more recent C standard just to make it compile, and (if that would be possible) automatically formatting that code to a more recent C version would introduce a hard "before/after" split in version control.
- uecker 3y ago
  What is wrong with "inline"? I do not think it is feasible to maintain all language versions in parallel for eternity. What would make porting this code to a newer standard difficult in this specific case?
  - flohofwoe 3y ago
    Inline "encourages" moving implementation code into headers instead of only interface declarations, and the inline feature isn't all that useful anymore with LTO anyway. It's a good thing to only have declarations in headers, it simplifies parsing with 3rd party tools (to generate language bindings), and speeds up compilation (see the C++ stdlib headers for the canonical "why is implementation code in headers a bad idea" example). IMHO mixing interface declarations with implementation details was one of the cardinal sins of C++. > What would make porting this code to a newer standard difficult in this specific case? It's pointless busywork, and it's unclear how deep the changes should go (for instance: does it make sense to move C89 variable declaration from the start of scope blocks to their initialization point just because it might potentially be "safer" but touches half of all lines of code?). The code demonstrably works as C89, and any bugs that matter most likely had already been fixed decades ago, also doing large scale syntax changes is just noise in version control which makes bug fixing harder (because that often involves diving into the change history).

by uecker 3y ago

sgbeal 3y ago

> I think we should try to transition code to the current ISO standard and in almost all cases this will just work without problems. In the few cases, where it does not, it is usually for a very good reason. Microsoft's C compiler did not support C99 until something like 15 years after the standard came out (and reportedly (according to colleagues who use that platform) still doesn't support certain features of it). It happens with surprising frequency that someone reports to the sqlite project that The Latest Version no longer works on their pre-2005 environment and they'd like to see it patched to work there. My point is: users of a given platform might not be able to use The Latest Stuff (or anywhere near it, for that matter) because their OS vendor is reticent, because they have to support an old platform which is not targeted by newer tools, or for whatever other reason. > Now, nobody is stopping compilers from supporting old language modes, but it adds a lot of complexity, ... i don't doubt that, and i do sympathize with the maintainers. i'm not saying they should never ever remove C89 support, but if they do then there needs to be an alternative, like a fork of the last compiler version which supported it, maintained at least to the extent that the rare genuine compiler bugs can be resolved.

uecker 3y ago
Microsoft declared C dead and wanted that everybody transitions to C++. Luckily this changed a bit and MSVC now supports newer standards. Also there are now other alternatives on Windows. So I do not think there is a good reason to put everything on standstill anymore. C needs to evolve and old code must be maintained. For me, this this means that code should be transitioned to newer standards. In no other industry would it be acceptable to ignore current industry standards. Now, I do understand that some projects do not want to use newer features for portability reasons. But this does not mean that they couldn't be compatible with a newer ISO C modes as well. Being compliant with C 17 does not necessarily mean one has to use new features.
pjmlp 3y ago
Microsoft considered C done, as clarified by Herb Sutter. https://herbsutter.com/2012/05/03/reader-qa-what-about-vc-and-c99/ https://herbsutter.com/2012/05/03/reader-qa-what-about-vc-an... They only kept updating their C support to the extent required by ISO C++ requirements, and some key customers. Anyone else still dependent on C was suggested to use clang, this is also why clang is part of Visual Studio compiler suite nowadays. Around the time the Microsoft <3 Linux stuff started, they decided to backtrack on this matter, and started updating their C support, however since C11 made a couple of stuff from C99 optional, they decided to skip on those. VLAs have anyway been proven a rich source of exploits, to the extent Google has sponsored the work to clean up the Linux kernel from all uses of them. https://www.phoronix.com/news/Linux-Kills-The-VLA https://www.phoronix.com/news/Linux-Kills-The-VLA
- uecker 3y ago
  The VLA security problems are a bit of a myth. In the kernel it may be some problem, but with stack clash protection (which one should activate anyway) there isn't really a inherent security issue anymore. The code quality improvements of using VLAs usually make it worth using them IMHO.
  - pjmlp 3y ago
    A myth that was worth every penny fixing it, as per Google.

flohofwoe 3y ago

I would rather just announce to the compiler what standard version a given piece of code should adhere to (and it's fine if -std=2x doesn't accept older C standards except for header declarations - while at it, please remove the 'inline' keyword from the next C standard ;)) To some extent that's already possible with the "-std=..." option of course, but it would be better to also allow changing the standard version within the same compilation unit (at least if it turns out that including headers written in old C standards can't be supported, in that case I would like to wrap a block of #includes with a 'use c89 { ... }'). Random example for why it is important to allow older C versions to compile: I just made a mid-90's assembler for 8-bit CPUs written in C89 work in VSCode via WASM/WASI without requiring any code changes (and yes I've been looking long and hard for an alternative assembler tool which provides the same feature set written more recently without luck, I even considered writing my own assembler from scratch). It would suck if I had to port the code base to a more recent C standard just to make it compile, and (if that would be possible) automatically formatting that code to a more recent C version would introduce a hard "before/after" split in version control.

uecker 3y ago
What is wrong with "inline"? I do not think it is feasible to maintain all language versions in parallel for eternity. What would make porting this code to a newer standard difficult in this specific case?
- flohofwoe 3y ago
  Inline "encourages" moving implementation code into headers instead of only interface declarations, and the inline feature isn't all that useful anymore with LTO anyway. It's a good thing to only have declarations in headers, it simplifies parsing with 3rd party tools (to generate language bindings), and speeds up compilation (see the C++ stdlib headers for the canonical "why is implementation code in headers a bad idea" example). IMHO mixing interface declarations with implementation details was one of the cardinal sins of C++. > What would make porting this code to a newer standard difficult in this specific case? It's pointless busywork, and it's unclear how deep the changes should go (for instance: does it make sense to move C89 variable declaration from the start of scope blocks to their initialization point just because it might potentially be "safer" but touches half of all lines of code?). The code demonstrably works as C89, and any bugs that matter most likely had already been fixed decades ago, also doing large scale syntax changes is just noise in version control which makes bug fixing harder (because that often involves diving into the change history).