Re: backtrace(3): Inconsistency and missing indentation

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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/
--
To unsubscribe from this list: send the line "unsubscribe linux-man" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html