Thanks, I think I'm getting it.

So is char* guaranteed to be the same width as sizeof(t_word)? If so, are you just using it as a shorthand?

Thanks,

Jonathan

On Monday, August 17, 2015 11:31 AM, Miller Puckette <msp@ucsd.edu> wrote:

Here's an example...

#include <stdio.h>

float foo[2];

main()
{
printf("foo = %p\n", foo);
printf("incremented as float: %p\n", foo+1);
printf("incremented as (char *): %p\n", ((char *)foo)+1);
}

--->

foo = 0x601038
incremented as float: 0x60103c
incremented as (char *): 0x601039

Adding an integer to a pointer "increments" it - the effect depends on the type
of pointer. Another way to think of it is that foo[1], say, is semantically
identical to *(foo+1).

cheers
Miller

On Mon, Aug 17, 2015 at 03:10:35PM +0000, Jonathan Wilkes via Pd-list wrote:
> But we're dealing with an array of t_words, so onset*sizeof(t_word) is what we want anyway, no?
> -Jonathan
>
>
> On Monday, August 17, 2015 10:55 AM, Claude Heiland-Allen <claude@mathr.co.uk> wrote:
>
>
> On 17/08/15 15:36, Jonathan Wilkes via Pd-list wrote:
> > Hi list,Wondering if someone will give me a free lesson in C programming.
> > In g_traversal.c, there's some code to retrieve a float from a t_word* vec. It looks like this:
> > *(t_float *)(((char *)vec) + onset));
> > Why does vec need to be cast to char*? t_word has to be as big as the largest member of the union, and the largest member has to be the same size as char*, right? (Otherwise we'd have big problems...)
>
> aiui pointer arithmetic is in increments of sizeof(pointee)
> if onset is measured in bytes (I don't know if it is in this case, but
> it looks likely), then you need to have a pointer to bytes for the
> addition to be meaningful. vec is already a pointer, but adding onset
> to a t_word* would offset the address by onset*sizeof(t_word) bytes
>
>
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