Well, after more testing, I found that my first version (labelled "frontal
attack") doesn't always work. Just in case anyone other than me cares, here's
a new version that seems to work properly. Sorry for the noise.
Boyd
// frontal attack
// testString = @"0756013";
testString = @"4756013";
// testString = @"0756";
// testString = @"0";
// alleles and digitsPerAllele are passed as arguments; the values shown
here are just for testing
int alleles = 3;
NSUInteger digitsPerAllele = 3;
NSString *subString;
NSRange range;
int theInt;
int i;
int sLength = [testString length];
range.location = 0;
int remainder = [testString length] % digitsPerAllele;
if (remainder > 0) {
range.length = remainder;
subString = [testString substringWithRange:range];
theInt = [subString intValue];
--alleles;
range.location = remainder;
sLength = sLength - remainder;
}
if (sLength > 0) {
range.length = digitsPerAllele;
for (i = 0; i < alleles; i++ ) {
subString = [testString substringWithRange:range];
theInt = [subString intValue];
range.location += digitsPerAllele;
}
}
Begin forwarded message:
> From: Boyd Collier <bcolli...@cox.net>
> Subject: Re: reverse scanner
> Date: August 12, 2013 1:00:56 PM PDT
> To: Cocoa Dev List <cocoa-dev@lists.apple.com>
>
> I've come up with a couple of reasonably straight-forward solutions to my
> problem, but first, thanks to everyone who offered suggestions. Even though I
> didn't choose to use them, your willingness to make them is definitely
> appreciated.
>
> Here are my solutions (note that there are 2, one labelled "attack from the
> rear", the other labelled "frontal attack"). I won't claim that they have
> been really thoroughly tested, but I have tried a variety of values for
> testString, d, digitsPerAllele and alleles and both methods appear to work.
> If anyone sees a problem or an improvements, please let me know. Right now,
> I favor the frontal attack, which occurred to me in the middle of the night
> -- I seldom have reason to use the % operator and so didn't think of it right
> away. Of course, in actual use, I'll first take steps to separate the string
> that's being processed into substrings, if the original string uses a ";"
> (for example) to separate allelic values, e.g. if the string being processed
> is 04;756;013.
>
> NSString *testString = @"0756013";
> NSUInteger d = 3;
> NSUInteger digitsPerAllele = d;
> NSUInteger alleles = 3;
>
> NSString *subString;
> NSRange range;
> int theInt;
>
> // attack from the rear
> int startOfRange = [testString length];
> int length = d;
> int i;
> for (i = 0; i < alleles; i++ ) {
> startOfRange = startOfRange-d;
> if (startOfRange < 0) {
> length = length + startOfRange; // note that startOfRange is
> negative here
> if (length <= 0)
> break;
> startOfRange = 0;
> d = length;
> }
> range.location = startOfRange;
> range.length = d;
> subString = [testString substringWithRange:range];
> theInt = [subString intValue];
> }
>
> // frontal attack
> testString = @"04756013";
> int remainder = [testString length] % digitsPerAllele;
> range.location = 0;
> range.length = remainder;
> subString = [testString substringWithRange:range];
> theInt = [subString intValue];
> --alleles;
> range.location = remainder;
> range.length = digitsPerAllele;
> for (i = 0; i < alleles; i++ ) {
> subString = [testString substringWithRange:range];
> theInt = [subString intValue];
> range.location += digitsPerAllele;
> }
>
>
> On Aug 10, 2013, at 10:07 AM, Boyd Collier <bcolli...@cox.net> wrote:
>
>> I'm dealing with a situation in which I have to scan strings that are
>> separated by tabs, and for each string, I have to extract two numerical
>> values, with these values being separated by a non-numerical character or
>> not being separated by any character at all. I know the maximum number of
>> characters used to represent each number, but unfortunately, the first
>> character in the group of characters used to represent the first number can,
>> quite arbitrarily, be either a 0 or missing. For example, with the number
>> of characters used to represent each number known to be 2, the strings 607,
>> 0607, 06;07 (note the semicolon between 06 and 07) should all result in 6
>> and 7 being extracted as the two numerical values. Of course, I'd like to do
>> something simple, and were it not for the arbitrary inclusion of a leading
>> 0, it would be quite simple to use an instance of NSScanner. Or, if there
>> were such a beast as NSReverseScanner, it would also be relatively straight
>> forward, but so far as I'm aware, no such beast exists. I can think of a
>> couple of ways do accomplish this task, but if someone has already come up
>> with a clean way of scanning in reverse, I'd appreciate hearing from them.
>>
>> Boyd
>
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