Re: [E-devel] alloca question

[Gustavo S. B. <bar...@pr...>]

On Tue, Jan 4, 2011 at 9:29 PM, Vincent Torri <vt...@un...> wrote:
>
>
> On Tue, 4 Jan 2011, Gustavo Sverzut Barbieri wrote:
>
>> On Tue, Jan 4, 2011 at 9:06 PM, Mike Blumenkrantz <mi...@ze...>
>> wrote:
>>>
>>> On Tue, 4 Jan 2011 20:03:47 -0200
>>> Gustavo Sverzut Barbieri <bar...@pr...> wrote:
>>>
>>>> On Tue, Jan 4, 2011 at 7:53 PM, Vincent Torri <vt...@un...>
>>>> wrote:
>>>>>
>>>>> On Tue, 4 Jan 2011, Mike Blumenkrantz wrote:
>>>>>
>>>>>> In my efm hacking, I've found a number of snippets like this:
>>>>>>
>>>>>>   size = strlen(v->udi) + 1;
>>>>>>   buf = alloca(size);
>>>>>>   strcpy(buf, v->udi);
>>>>>>   ecore_ipc_server_send(_e_fm_ipc_server,
>>>>>>                         6 /*E_IPC_DOMAIN_FM*/,
>>>>>>                         E_FM_OP_EJECT_DONE,
>>>>>>                         0, 0, 0, buf, size);
>>>>>>
>>>>>> Is there a reason why we can't just use strdupa?  It should be about
>>>>>> as
>>>>>> portable as alloca...
>>>>>
>>>>> strdupa is not portable at all. It is part of the glibc (it's a GNU
>>>>> stuff).
>>>>
>>>> given that the above code does exactly what strdupa() would do, why
>>>> not use it and save lines, defining a strdupa() macro where not
>>>> available?
>>>>
>>>> something like this should do:
>>>>
>>>> #define stdupa(str) strcpy(alloca(strlen(str) + 1), str)
>>>>
>>>>
>>> seems fairly reasonable, assuming it's portable?
>>
>> according to manpages it is portable given that alloca exists.
>
> no, it's not:
>
> http://linux.die.net/man/3/strdupa
>
> "strdupa() and strndupa() are similar, but use alloca(3) to allocate the
> buffer. They are only available when using the GNU GCC suite, and suffer
> from the same limitations described in alloca(3)."
>
> So strdupa() is defined only in glibc. It does not exist on Windows for
> example.

Vincent, read again. I said that this macro is a portable solution to
the lack of strdupa():

#define stdupa(str) strcpy(alloca(strlen(str) + 1), str)



-- 
Gustavo Sverzut Barbieri
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