On 2005-07-17 12:55:38 -0400, Paul Koning wrote:
> Are you sayinvg that a-b is not always "guaranteed to work" when a
> and b point to elements of the same array? That sounds wrong; can
> you given an example or standards text that supports this?
6.5.6 Additive operators
[...]
[#9] When two pointers are subtracted, both shall point to
elements of the same array object, or one past the last
element of the array object; the result is the difference of
the subscripts of the two array elements. The size of the
result is implementation-defined, and its type (a signed
integer type) is ptrdiff_t defined in the <stddef.h> header.
If the result is not representable in an object of that
type, the behavior is undefined. In other words, if the
expressions P and Q point to, respectively, the i-th and j-
th elements of an array object, the expression (P)-(Q) has
the value i-j provided the value fits in an object of type
ptrdiff_t. [...]
See the sentence "If the result..." and the last few words of the
next sentence.
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Vincent Lefèvre <[EMAIL PROTECTED]> - Web: <http://www.vinc17.org/>
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Work: CR INRIA - computer arithmetic / SPACES project at LORIA
