Joerg Wunsch wrote:
David Brown <david.br...@hesbynett.no> wrote:
Secondly, using pointer arithmetic when array access is the
logically correct method is very bad practice.
That's often a matter of taste. Once you grasped the C pointer
semantics, I usually find
foo + i
much easier to parse than
&foo[i].
Both expressions are always equivalent.
Of course,
*(foo + i)
is terrible, because
foo[i]
is much clearer then.
Anyway, for the compiler, it should never make any difference, because
these expressions are identical in their effect. If the compiler can
(statically) bounds-check &foo[i], I don't see why it would not be
able doing so for foo + i. (Most of the time, it cannot check it
though.)
The two expressions (foo + i) and &foo[i] are *not* equivalent, because
one is a pointer arithmetic expression and the other is taking the
address of an element of an array. They should boil down to the same
calculations (the C standard says so). However, the compiler has a much
better chance of doing bounds checking, alias checking, and other
optimisations on the array expression. It is even free to reorganise
the array, or keep it all in registers (I don't think any compilers do
that, but maybe one day...), whereas working with raw addresses will
often cause the compiler to lose the extra knowledge of the array.
Recent improvements in gcc include keeping the array information further
into the code generation process (rather than generating pointer
arithmetic) for this reason, as far as I understand (I could be wrong
here - you are the expert!).
Additionally, &foo[i] and (foo + i) read as different things (one is the
address of an element, the other is the address of an array plus an
offset). To my mind, these are different and I'd use them in different
types of code.
Finally, if you are using C++ rather than C, using array notation allows
overloading to make types that work logically as arrays without
necessarily being a contiguous block of memory.
mvh.,
David
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