Re: How to check if char pointer is a constant!?

["Daniel." <danielhilst@gmail.com>]

Hi Phil,

Yes I could use strduped strings to avoid this case but at this point
I just want to
have sure that if I do that mistake in future (trying to change a
const str *) the compiler at
last warns me about it :). In the real case this function is called
with a buffer from a readed
file so that it's first parameter aways point to valid lvalue data,
but I (or other) may change the code
in future and try to call it with string constants, I would like to
prevent my self from doing
that and if it happen have a better clue of what happen. Your anwser
apply just as I expected.

Cheers,

2016-07-08 9:59 GMT-03:00 Phil Sutter <phil@nwl.cc>:
> On Fri, Jul 08, 2016 at 09:33:03AM -0300, Daniel. wrote:
>> Hi all thanks for the reply.
>>
>> I think I wasn't clear. Here is a working example: http://codepad.org/0SUG6IcQ
>>
>> The function get_pair_from_string() should I) remove trailing spcaes, II) return
>> the address for key and value using it's last parameters. The problem is that
>> since I modify the first parameter calling with strings constants generates a
>> segmentation fault. This is because strings constans aren't modifiable. I wan't
>> to have better hints when this happen than just "SEGSEGV". I think that the
>> -Wwrite-strings is what I was looking for :D, thanks Phil!!!
>
> Glad I could help.
>
>> John, I'll be in production, but not at this time. Luckly, that
>> function is file scoped
>> so I don't have to bother that much. Still I like to avoid the crypt
>> "SEGSEGV" error
>> message as much as possible. Usually I assert for NULL pointers and give a nice
>> error message but this case is trickier. I'll take Phil advice and use
>> -Wwrite-strings
>
> Calling 'SIGSEGV' an error message is a slight underestimation. Actually
> your program simply crashes. The gcc warning to activate will just help
> to keep your code sane, not improve run-time behaviour.
>
> If you want to modify strings no matter whether they are constant or
> not, strdup() them into a local variable and work with that. Especially
> since it's just for parsing as your example shows. Just keep in mind
> that you will have to free the duplicated string at some point,
> otherwise you will have a memory leak (which at some point will lead to
> an equally cryptic message as your segfault did).
>
> Cheers, Phil



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