On Mon, 10 Sep 2012 13:08:29 -0400, Benjamin Thaut
<[email protected]> wrote:
The following code
bool endsWith(string str, string end)
{
size_t to = str.length - end.length;
for(sizediff_t i = str.length - 1; i >= to; --i)
{
if(str[i] != end[i-to])
return false;
}
return true;
}
int main(string[] args)
{
return cast(int)endsWith("blub", "blub");
}
compiled with dmd 2.060 gives me a range violation. (with i = -1)
although it shouldn't. If I change to from size_t "to" sizediff_t
everything is fine. The comparison between the unsigned "to" and the
signed "i" is not done correctly.
Is this a code gen bug? Or is it missing a compiler warning / error? Or
is this entierly my fault?
It is behaving as expected.
through integer promotion rules, i >= to is converted to unsigned
comparison. So if i becomes -1, then it really becomes a comparison
between 2^32 - 1 and 0.
In other words, if to is 0, then the loop will never terminate (because
unsigned can never be less than 0).
The solution is to re-design your loop. I try to avoid conditions that
could be done with negative values for the above reason.
sizediff_t offset = str.length - end.length;
for(sizediff_t i = 0; i < end.length; ++i)
{
if(str[offset + i] != end[i])
return false;
}
return true;
Or if you want to skip all this, you can just use the wonderful D slice
syntax :)
if(str.length > end.length)
return str[$-end.length..$] == end;
else
return false;
-Steve
