Ytukyg

Is it possible to see of a string ends with a number which length is not known?

1. "String 1" -> 1


2. "String 4356" -> 4356


3. "String" -> nil

If so, how can I determine that number?

To test that a string ends with numbers, you can use an NSPredicate, such as:

NSPredicate endsNumerically = [NSPredicate predicateWithFormat:@"SELF matches %@", @"\d+$"];

[endsNumerically evaluateWithObject:string]; // returns TRUE if predicate succeeds

NSScanner is sometimes useful for extracting things from strings, but it doesn't scan backward. You could define a Gnirts (reverse string) class and use that with an NSScanner, but that's probably more hassle than it's worth.

NSString's rangeOfCharacterFromSet:options:, which I had hope to use, only looks for a single character (it's like strchr and strrchr, if you're familiar with C), but we can roll our own that returns a contiguous range of characters from a set (a little like strspn) as a category on NSString. While we're at it, let's include methods that return substrings rather than ranges.

RangeOfCharacters.h:

@interface NSString (RangeOfCharacters)

/* note "Characters" is plural in the methods. It has poor readability, hard to 

 * distinguish from the rangeOfCharacterFromSet: methods, but it's standard Apple 

 * convention.

 */

-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet;

-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask;

-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask range:(NSRange)range;



// like the above, but return a string rather than a range

-(NSString*)substringFromSet:(NSCharacterSet*)aSet;

-(NSString*)substringFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask;

-(NSString*)substringFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask range:(NSRange)range;

@end

RangeOfCharacters.m:

@implementation NSString (RangeOfCharacters)

-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet {

    return [self rangeOfCharactersFromSet:aSet options:0];

}



-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask {

    NSRange range = {0,[self length]};

    return [self rangeOfCharactersFromSet:aSet options:mask range:range];

}



-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask range:(NSRange)range {

    NSInteger start, curr, end, step=1;

    if (mask & NSBackwardsSearch) {

        step = -1;

        start = range.location + range.length - 1;

        end = range.location-1;

    } else {

        start = range.location;

        end = start + range.length;

    }

    if (!(mask & NSAnchoredSearch)) {

        // find first character in set

        for (;start != end; start += step) {

            if ([aSet characterIsMember:[self characterAtIndex:start]]) {

#ifdef NOGOTO

                break;

#else

                // Yeah, a goto. If you don't like them, define NOGOTO.

                // Method will work the same, it will just make unneeded

                // test whether character at start is in aSet

                goto FoundMember;

#endif

            }

        }

#ifndef NOGOTO

        goto NoSuchMember;

#endif

    }

    if (![aSet characterIsMember:[self characterAtIndex:start]]) {

    NoSuchMember:

        // no characters found within given range

        range.location = NSNotFound;

        range.length = 0;

        return range;

    }



FoundMember:

    for (curr = start; curr != end; curr += step) {

        if (![aSet characterIsMember:[self characterAtIndex:curr]]) {

            break;

        }

    }

    if (curr < start) {

        // search was backwards

        range.location = curr+1;

        range.length = start - curr;

    } else {

        range.location = start;

        range.length = curr - start;

    }

    return range;

}



-(NSString*)substringFromSet:(NSCharacterSet*)aSet {

    return [self substringFromSet:aSet options:0];

}



-(NSString*)substringFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask  {

    NSRange range = {0,[self length]};

    return [self substringFromSet:aSet options:mask range:range];

}

-(NSString*)substringFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask range:(NSRange)range {

    NSRange range = [self rangeOfCharactersFromSet:aSet options:mask range:range];

    if (NSNotFound == range.location) {

        return nil;

    }

    return [self substringWithRange:range]; 

}

@end

To use the new category to check that a string ends with digits or to extract the number:

NSString* number = [string substringFromSet:[NSCharacterSet decimalDigitCharacterSet] 

                             options:NSBackwardsSearch|NSAnchoredSearch];

if (number != nil) {

    return [number intValue];

} else {

    // string doesn't end with a number.

}

Lastly, you can use a third party regular expression library, such as RegexKit or RegexkitLite.

I couldn't get the NSPredicate code above to work correctly, though it looks like it should. Instead I accomplished the same thing with

if ([string rangeOfString:@"\d+$" options:NSRegularExpressionSearch].location != NSNotFound) {

    // string ends with a number

}

Hat-tip to this answer.