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
