Re: Need help with C syntax in examples from 'Learning Core Audio' book
Re: Need help with C syntax in examples from 'Learning Core Audio' book
- Subject: Re: Need help with C syntax in examples from 'Learning Core Audio' book
- From: "Raimondas K." <email@hidden>
- Date: Fri, 18 May 2012 21:54:46 -0400
On Wed, May 16, 2012 at 7:29 AM, Brian Lambert <email@hidden> wrote:
> It is taking the value of error and converting it from the host’s native
> byte order to big-endian format.
> CFSwapInt32HostToBig(error);
>
> It then writes the binary value of the error in big-endian format to bytes
> 1,2,3,4 of the 20 character error string.
>
> (errorString + 1) is a pointer to byte 1 of the 20 character string.
>
> (UInt32 *)(errorString + 1) casts this pointer to be a pointer to a UInt32.
>
> *(UInt32 *)(errorString + 1) dereferences this UInt32 pointer, allowing it
> to be used as an l-value.
I am surprised this actually works -- no byte alignment issues?
=R.
>
> So, this allows one to assign the UInt32 value
> of CFSwapInt32HostToBig(error) into bytes 1,2,3,4 of the 20 character error
> string as though it was a UInt32.
>
> Then the code goes on to examine the bytes using isprint.
>
>
> On Wed, May 16, 2012 at 4:00 AM, Ben <email@hidden>
> wrote:
>>
>> I'm running through the examples in the book 'Learning Core Audio' and I
>> came across these two lines...
>>
>>
>> char errorString[20];
>> // see if it appears to be a 4-char-code
>> *(UInt32 *)(errorString + 1) = CFSwapInt32HostToBig(error);
>>
>> The second line looks pretty alien to me (rusty on C), can someone explain
>> what is going on please? I understand what the function
>> CFSwapInt32HostToBig() is doing, but what is going on with errorString?
>>
>> Thanks in advance.
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