On 19 Nov 2006, at 15:45, Graham J Lee wrote:
Hi,
I'm trying to implement NSNumberFormatter's -stringForObjectValue:
as I said on bug-. However, I'm having trouble with parsing the
format string and I expect it has more to do with my confusion than
it does with any other problems ;-).
The Cocoa behaviour for the formatter is that if the character '.'
appears anywhere in the format string, this "turns on" displaying
the fractional part of the number (unless allowsFloats is false)
with as many decimal places as the are placeholder characters (# or
a number) to the *immediate* right of the *rightmost* '.' in the
format string. So I'm doing this:
if ([self allowsFloats] && (NSNotFound != [useFormat
rangeOfString:@"." ].location))
{
decimalPlaceRange = [useFormat rangeOfString: @"." options:
NSBackwardsSearch];
while ([placeHolders characterIsMember: [useFormat
characterAtIndex: NSMaxRange(decimalPlaceRange)]])
{
decimalPlaceRange.length++;
if (NSMaxRange(decimalPlaceRange) == [useFormat length])
break;
}
decimalPlaces=decimalPlaceRange.length;
if (0 != decimalPlaces)
displayFractionalPart = YES;
}
which doesn't work...decimalPlaces ends up being some garbage value
such as 2412439 when the length of the string is only, say, 7. For
that to happen then the length of the *range* must have always been
greater than the length of the string (so that the if(NSMaxRange
(...)...) line never breaks the loop) and the loops *starts* by
reading nonsense memory outside the string. Why would that happen?
It's hard to tell without a complete test program ... but I can make
a couple of observations.
1. the loop should not be able to start by 'reading nonsense memory
outside the string' because the -characterAtIndex: method should
raise an exception if asked to refer to an index outside the string.
2. if useFormat is nil then the code is totally broken since sending
a message to a nil object is defined to return nil ... but where the
method is expected to return a range this means that the resulting
behavior is undefined. On sparc it will cause an immediate crash,
but on intel I think it probably just means the returned range
contains garbage ... which would explain your symptoms.
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