Re: Is there a more efficient way to get the first 4 bytes off a NSInputStream to compare
Re: Is there a more efficient way to get the first 4 bytes off a NSInputStream to compare
- Subject: Re: Is there a more efficient way to get the first 4 bytes off a NSInputStream to compare
- From: Graham Cox <email@hidden>
- Date: Wed, 28 Jan 2009 10:07:57 +1100
On 28 Jan 2009, at 2:24 am, Jeremy Pereira wrote:
Yes. That is correct, but since buffer is already a pointer to the
first byte of the array and then you are taking a reference to it,
key will end up containing the address of the buffer. You really
need:
uint key = *(uint*)buffer;
That's incorrect. Or rather, in this case it doesn't make any
difference, but the use of '&' is more general as it works whether
buffer is an array or not.
When you declare:
uint8 buffer[8];
You've reserved 8 bytes on the stack. Whether you use 'buffer' or
'&buffer' you obtain the same address, as C treats array variables as
pointers. But:
uint8 buffer;
You get very different results from 'buffer' and '&buffer' so in the
interests of defensive programming, using '&' is allowing your code to
tolerate a change to the buffer declaration without breaking. Because
of the additional cast *(int*) such a change would go unnoticed by the
compiler but probably have a very bad outcome at runtime. It's a good
habit IMO to always take the address in these cases to make it clear
in your code what your intentions were when you wrote it.
--Graham
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