Thomas said:
Read ISO9899:1999 section 6.5.6 paragraph 8:
<quote>
When an expression that has integer type is added to or subtracted from
a pointer, the
result has the type of the pointer operand. If the pointer operand
points to an element of
an array object, and the array is large enough, the result points to an
element offset from
the original element such that the difference of the subscripts of the
resulting and original
array elements equals the integer expression. In other words, if the
expression P points to
the i-th element of an array object, the expressions (P)+N
(equivalently, N+(P)) and
(P)-N (where N has the value n) point to, respectively, the i+n-th and
i−n-th elements of
the array object, provided they exist. Moreover, if the expression P
points to the last
element of an array object, the expression (P)+1 points one past the
last element of the
array object, and if the expression Q points one past the last element
of an array object,
the expression (Q)-1 points to the last element of the array object. If
both the pointer
operand and the result point to elements of the same array object, or
one past the last
element of the array object, the evaluation shall not produce an
overflow; otherwise, the
behavior is undefined. If the result points one past the last element of
the array object, it
shall not be used as the operand of a unary * operator that is evaluated.
</quote>
especially the last two sentences...
Tom
sorry that was the wrong standard...
but in ISO14882 section 5.7 paragraph 5 the text is almost the same:
<quote>
When an expression that has integral type is added to or subtracted from
a pointer, the result has the type of
the pointer operand. If the pointer operand points to an element of an
array object, and the array is large
enough, the result points to an element offset from the original element
such that the difference of the subscripts
of the resulting and original array elements equals the integral
expression. In other words, if the
expression P points to the i-th element of an array object, the
expressions (P)+N (equivalently, N+(P))
and (P)-N (where N has the value n) point to, respectively, the i+n-th
and i–n-th elements of the array
object, provided they exist. Moreover, if the expression P points to the
last element of an array object, the
expression (P)+1 points one past the last element of the array object,
and if the expression Q points one
past the last element of an array object, the expression (Q)-1 points to
the last element of the array object.
If both the pointer operand and the result point to elements of the same
array object, or one past the last element
of the array object, the evaluation shall not produce an overflow;
otherwise, the behavior is undefined.
</quote>
Tom