iphone - Get String Between Two Other Strings in ObjC

Question

I am trying to parse a string and get another string in the middle.

ie.

Hello world this is a string

I need to find the string between "world" and "is" (this). I have looked around but haven't been able to figure it out yet, mainly because I am new to Objective C... Anyone have an idea of how to do this, with RegEx or without?

Answer 1

The regular expressions solution that Jacques gives works, and the caveat of requiring iOS 4.0 and later is true. Using regular expressions is also quite slow, and an overkill if the search expressions are known string constants.

You can solve the problem using methods on NSString, or a class named NSScanner, both have been available since iPhone OS 2.0 and long before that, since before Mac OS X 10.0 actually :).

So what you want is a new method on NSString like this?

@interface NSString (CWAddition)
- (NSString*) stringBetweenString:(NSString*)start andString:(NSString*)end;
@end

No problem, and we assume we should return nil is no such strings could be found.

The implementation using NSString only is quite straight forward:

@implementation NSString (NSAddition)
- (NSString*) stringBetweenString:(NSString*)start andString:(NSString*)end {
    NSRange startRange = [self rangeOfString:start];
    if (startRange.location != NSNotFound) {
        NSRange targetRange;
        targetRange.location = startRange.location + startRange.length;
        targetRange.length = [self length] - targetRange.location;   
        NSRange endRange = [self rangeOfString:end options:0 range:targetRange];
        if (endRange.location != NSNotFound) {
           targetRange.length = endRange.location - targetRange.location;
           return [self substringWithRange:targetRange];
        }
    }
    return nil;
}
@end

Or you could do the implementation using the NSScanner class:

@implementation NSString (NSAddition)
- (NSString*) stringBetweenString:(NSString*)start andString:(NSString*)end {
    NSScanner* scanner = [NSScanner scannerWithString:self];
    [scanner setCharactersToBeSkipped:nil];
    [scanner scanUpToString:start intoString:NULL];
    if ([scanner scanString:start intoString:NULL]) {
        NSString* result = nil;
        if ([scanner scanUpToString:end intoString:&result]) {
            return result;
        }
    }
    return nil;
}
@end