On Fri, Feb 26, 2016 at 7:46 AM, Michael Kerrisk (man-pages)
<mtk.manpages@xxxxxxxxx> 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. The code won't compile with "gcc -pedantic-errors".
Given the need to support C90, I suggest that the #define is still
the best way to define the constant. You could use an enum hack:
enum { size = 100 };
void *buffer[size];
but that's a little obscure, and introduces an issue that's not
relevant to the backtrace() function.
--
Keith Thompson <Keith.S.Thompson@xxxxxxxxx>
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