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According to the C spec, zero length arrays are explicitly illegal. > Zero-length array declarations are not allowed, even though some compilers offer them as

According to the C spec, zero length arrays are explicitly illegal. > Zero-length array declarations are not allowed, even though some compilers offer them as extensions (typically as a pre-C99 implementation of flexible array members). However, as they say, gcc (and therefore clang) have an extension that allows it. So does MSVC but it works slightly differently.

fsckboy 4y ago
you should be specific about which C spec you are referring to, you talk about "the C spec" and then you mention the "pre-C99 implementation". Maybe you mean they've always been illegal in every version, but it would be more clear.
- deleted 4y ago
  [deleted]
- ChrisSD 4y ago
  The bit after `>` is a quote, not my words. See https://en.cppreference.com/w/c/language/array https://en.cppreference.com/w/c/language/array for the source It's saying that C99 implemented flexible array members but before then some compilers introduced their own (nonstandard) implementation of flexible array members, using the (not allowed) zero sized array notation.
  - segfaultbuserr 4y ago
    The sequence of event was basically: 1. Pre-C99, no flexible array was allowed. 2. Gradually, people started using the "size-1 array at the end of a sturct but write beyond" hack as flexible array. 3. As an attempt to do the hack in a more ordered manner, some compilers, including GCC, started officially supporting the non-standard "size-0" array extension. 4. C99 added flexible array with indefinite length (array[]), while prohibiting both the undefined-behavior "array[1]" and the non-standard extentios "array[0]". So when people say "size-0" array, it could mean either of these three things, and it does get a bit confusing. But fundamentally the idea was the same, all of the three techniques are used to achieve the same practical effect.
- alerighi 4y ago
  In reality, who cares of what the C spec says? Unless you have to port code on different compilers (which is very unlikely, unless you are building a library meant to be shared with different projects) you only care about the fact that the code works correctly with the compiler you choose to use. I don't get all the programmers that scandalize if you use GNU extensions, they are fine, and mostly useful, so if you are using GCC to program I don't see why not use -std=gnu11 instead of -std=c11... who cares if the program is not compliant? Even if you want to be compliant to share code, the C standard is you last problem, the thing is that you probably use a ton of libraries and header files specific to that implementation (such as POSIX or even worse Linux-specific stuff), so your code is 99% not portable anyway without rewriting most of it.
  - andreareina 4y ago
    It’s all well and good until someone else wants to compile it on clang[1]. There’s a lot of value in C being a lingua franca of sorts, and that depends on a cross-implementation understanding of semantics, i.e. standards, (though that doesn’t have to be from whatever official body that produced C99 etc). [1] IIRC on OSX[2] gcc actually invokes clang [2] stopped upgrading before it became macOS
    - astrange 4y ago
      Clang implements nearly all GCC extensions. (No nested functions.)

fsckboy 4y ago

you should be specific about which C spec you are referring to, you talk about "the C spec" and then you mention the "pre-C99 implementation". Maybe you mean they've always been illegal in every version, but it would be more clear.

deleted 4y ago
[deleted]
ChrisSD 4y ago
The bit after `>` is a quote, not my words. See https://en.cppreference.com/w/c/language/array https://en.cppreference.com/w/c/language/array for the source It's saying that C99 implemented flexible array members but before then some compilers introduced their own (nonstandard) implementation of flexible array members, using the (not allowed) zero sized array notation.
- segfaultbuserr 4y ago
  The sequence of event was basically: 1. Pre-C99, no flexible array was allowed. 2. Gradually, people started using the "size-1 array at the end of a sturct but write beyond" hack as flexible array. 3. As an attempt to do the hack in a more ordered manner, some compilers, including GCC, started officially supporting the non-standard "size-0" array extension. 4. C99 added flexible array with indefinite length (array[]), while prohibiting both the undefined-behavior "array[1]" and the non-standard extentios "array[0]". So when people say "size-0" array, it could mean either of these three things, and it does get a bit confusing. But fundamentally the idea was the same, all of the three techniques are used to achieve the same practical effect.
alerighi 4y ago
In reality, who cares of what the C spec says? Unless you have to port code on different compilers (which is very unlikely, unless you are building a library meant to be shared with different projects) you only care about the fact that the code works correctly with the compiler you choose to use. I don't get all the programmers that scandalize if you use GNU extensions, they are fine, and mostly useful, so if you are using GCC to program I don't see why not use -std=gnu11 instead of -std=c11... who cares if the program is not compliant? Even if you want to be compliant to share code, the C standard is you last problem, the thing is that you probably use a ton of libraries and header files specific to that implementation (such as POSIX or even worse Linux-specific stuff), so your code is 99% not portable anyway without rewriting most of it.
- andreareina 4y ago
  It’s all well and good until someone else wants to compile it on clang[1]. There’s a lot of value in C being a lingua franca of sorts, and that depends on a cross-implementation understanding of semantics, i.e. standards, (though that doesn’t have to be from whatever official body that produced C99 etc). [1] IIRC on OSX[2] gcc actually invokes clang [2] stopped upgrading before it became macOS
  - astrange 4y ago
    Clang implements nearly all GCC extensions. (No nested functions.)