*char is guaranteed to be the same size as a 'char', 8 bits -- but if you're treating t_word as an array of char's, you can get into t_word and process it in 8 bit chunks.
On Mon, Aug 17, 2015 at 9:53 AM, Jonathan Wilkes via Pd-list < [email protected]> wrote: > Ah, ok-- I forgot my pointer arithmetic rules. > Once I remembered how it works, I still wasn't understanding how you could > be doing pointer arithmetic with byte granularity when t_word is wider than > 1 byte. But then I see from template_find_field you are multiplying the > onset by sizeof(t_word). > > So now, further down the rabbit hole of knowledge, I'm wondering why you > multiply by sizeof(t_word) at all. If you didn't, couldn't the (char *) > cast go away? > > -Jonathan > > > > On Monday, August 17, 2015 12:24 PM, Miller Puckette <[email protected]> wrote: > > > I don't thing the width of (char *) enters into it (it's a pointer, 8 > chars in > 64 bit addr space) - the direct contrast to be made is (char) vs (t_word). > > Not sure if that answers the question though... > > cheers > M > > On Mon, Aug 17, 2015 at 03:52:27PM +0000, Jonathan Wilkes via Pd-list > wrote: > > 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 <[email protected]> > 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 < > [email protected]> 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 > > > > > > > > > _______________________________________________ > > > [email protected] mailing list > > > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > > > > > > > > > > > > > > _______________________________________________ > > > [email protected] mailing list > > > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > > > > > > > > > > > _______________________________________________ > > [email protected] mailing list > > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > > > > > _______________________________________________ > [email protected] mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > >
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