array[-1] -- permitted?

[David Keppel]

djones at megatest.UUCP (Dave Jones) writes:
>[ yacc example ]


The C standard does not tsy that computing a negative offset off of
a pointer is illegal, it says that computing one that is outside of
the array that the pointer points in to (the a single object is an
array of size 1) iis not standard C.

In the case of the YACC example, consider the following:

    int a[10];
    int *ip;

    ip = &a[0];

    &ip[-1];	/* iplementation-defined behavior */
    &ip[0];	/* just fine */
    &ip[9];	/* just fine */
    &ip[10];	/* just fine */
    ip[10];	/* iplementation-defined behavior */

    ip = &a[5];

    &ip[-6];	/* iplementation-defined behavior */
    &ip[-5];	/* just fine */
    &ip[4];	/* just fine */
    &ip[5];	/* just fine */
    ip[5];	/* iplementation-defined behavior */

And that's the way it is.

	;-D on  ( My goodness and my badness )  Pardo
-- 
		    pardo at cs.washington.edu
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