Re: Why std::size_t instead of int? (was Re: Do I really have to
use an array?)
* Andrew Koenig:
"Alf P. Steinbach" <alfps@start.no> wrote in message
news:13qjhorqbs7rkc3@corp.supernews.com...
If you want the range myLenght-1 downto 0, inclusive, consider just
for( size_t i = myLength-1; i != size_t(-1); --i )
I have to say that this example is too clever for my taste. I'd rather
write:
for (size_t i = myLength; i != 0; ) {
--i;
// whatever
}
I have to say that that example is too clever for /my/ taste... ;-)
With a for-loop, except "for(;;)", one expects the expression that in
some sense "counts" (or less informally speaking, controls the loop
variant), to be in the loop head, after that last semicolon.
Also, one expects the initializer to be the first value for the loop
control variable.
One reason for my preference is that this technique works for bidirectional
iterators too:
for (list<T>::iterator it = myList.end(); it != myList.begin(); ) {
--it;
// whatever
}
whereas the "myLength-1" technique doesn't.
Hm. I don't think it's necessarily a good idea to press different kinds
of code into the same form, or using the possibility of doing so as a
positive guideline. And I think the above would be better expressed
using reverse iterators, placing the update in the for loop head, like
typedef list<T>::reverse_iterator RIterator;
for( RIterator it = myList.rbegin(); it != myList.rend(); ++it )
{
// Whatever
}
And just an idea, essentially the same can be accomplished for integer
indices,
#include <cstddef>
#include <iostream>
struct RIndex
{
size_t current;
size_t end;
RIndex( size_t firstValue, size_t lastValue = 0 )
: current( firstValue ), end( lastValue - 1 )
{}
operator size_t() const { return current; }
bool atEnd() const { return (current == end); }
void advance() { --current; }
};
int main()
{
using namespace std;
static int const myList[] = {1, 2, 3};
static size_t const myLength =
sizeof(myList)/sizeof(*myList);
for( RIndex i = myLength-1; !i.atEnd(); i.advance() )
{
cout << myList[i] << endl;
}
}
where not using the iterator idiom (operator*, operator++) is
intentional, since it's not really an iterator.
Cheers,
- Alf
--
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