Re: NSMutableData +dataWithLength: sets errno?
Re: NSMutableData +dataWithLength: sets errno?
- Subject: Re: NSMutableData +dataWithLength: sets errno?
- From: Carl Hoefs <email@hidden>
- Date: Tue, 14 Mar 2017 16:30:53 -0700
> On Mar 14, 2017, at 4:27 PM, Greg Parker <email@hidden> wrote:
>
>>
>> On Mar 14, 2017, at 4:08 PM, John McCall <email@hidden <mailto:email@hidden>> wrote:
>>
>>> On Mar 14, 2017, at 7:00 PM, Carl Hoefs <email@hidden <mailto:email@hidden>> wrote:
>>> macOS 10.12.3, Xcode 8.2.1, ObjC
>>>
>>> I'm finding the following line to be problematic:
>>>
>>> NSMutableData *myData = [NSMutableData dataWithLength:80];
>>>
>>> I assume this ends up calling calloc(3) to allocate and zero out the data. But for some reason, it's always setting errno to a seemingly random nonzero value, generally either errno=2 (ENOENT) or errno=22 (EINVAL).
>>>
>>> Now that I know it does this, I can make accommodations for it, but is this expected behavior?
>>
>> I don't know why it's happening here, but unless you're calling a function that specifically documents its errno behavior, you should assume that every call you make might randomly overwrite errno with gibberish.
>
> The POSIX standard specifically states that errno's value is undefined almost everywhere and can be arbitrarily changed by almost anything.
>
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/errno.html <http://pubs.opengroup.org/onlinepubs/9699919799/functions/errno.html>
>
Thanks, John & Greg. I simply wasn't aware of this!
-Carl
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