Re: backtrace(3): Inconsistency and missing indentation

[Keith Thompson <keithsthompson-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Sorry, I meant "gcc -ansi -pedantic".

On Fri, Feb 26, 2016 at 12:35 PM, Michael Kerrisk (man-pages)
<mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Hi Keith,
>
> On 02/26/2016 08:52 PM, Keith Thompson wrote:
>> On Fri, Feb 26, 2016 at 7:46 AM, Michael Kerrisk (man-pages)
>> <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>>> On 02/24/2016 10:26 AM, Martin Gebert wrote:
>>>> In the example section of the page the following snippet is given:
>>>>
>>>> --8><--
>>>>         void
>>>>         myfunc3(void)
>>>>         {
>>>>             int j, nptrs;
>>>>         #define SIZE 100
>>>>             void *buffer[100];
>>>>             char **strings;
>>>>
>>>>             nptrs = backtrace(buffer, SIZE);
>>>> --><8--
>>>>
>>>> Problems:
>>>>
>>>>  1. "#define SIZE 100" is not indented correctly.
>>>>  2. SIZE should also be used for the buffer array size.
>>>
>>> Thanks, Martin. Fixed as below.
>>>
>>> Cheers,
>>>
>>> Michael
>>>
>>> diff --git a/man3/backtrace.3 b/man3/backtrace.3
>>> index afca93d..064b970 100644
>>> --- a/man3/backtrace.3
>>> +++ b/man3/backtrace.3
>>> @@ -215,8 +215,8 @@ void
>>>  myfunc3(void)
>>>  {
>>>      int j, nptrs;
>>> -#define SIZE 100
>>> -    void *buffer[100];
>>> +    const int SIZE = 100;
>>> +    void *buffer[SIZE];
>>>      char **strings;
>>>
>>>      nptrs = backtrace(buffer, SIZE);
>>
>> I suggest leaving it as it was, apart from using SIZE in the definition
>> of buffer.
>>
>> It's common for preprocessor directives to be left-justified rather
>> than aligned with the surrounding code.  (They mostly appear at file
>> scope, so it's not usually an issue.)  It's perfectly valid to indent
>> the #define, but it's a bit misleading, since it implies that SIZE has
>> a scope (it doesn't, it's visible to the end of the translation unit).
>>
>> With the "const int" declaration, buffer becomes a VLA (variable
>> length array).  VLAs don't exist in C90, do exist in C99, and are
>> optional in C11.
>
> Ahhh -- I was not aware of the C11 detail.
>
>> The code won't compile with "gcc -pedantic-errors".
>
> Which gcc versions do that? I do not see such an error from gcc 5.3.
>
> Cheers,
>
> Michael
>
>
>
>
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/



-- 
Keith Thompson <Keith.S.Thompson-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
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