objective c - How to get substring of NSString?

Question

If I want to get a value from the NSString @"value:hello World:value", what should I use?

The return value I want is @"hello World".

Answer 1

Option 1:

NSString *haystack = @"value:hello World:value";
NSString *haystackPrefix = @"value:";
NSString *haystackSuffix = @":value";
NSRange needleRange = NSMakeRange(haystackPrefix.length,
                                  haystack.length - haystackPrefix.length - haystackSuffix.length);
NSString *needle = [haystack substringWithRange:needleRange];
NSLog(@"needle: %@", needle); // -> "hello World"

Option 2:

NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"^value:(.+?):value$" options:0 error:nil];
NSTextCheckingResult *match = [regex firstMatchInString:haystack options:NSAnchoredSearch range:NSMakeRange(0, haystack.length)];
NSRange needleRange = [match rangeAtIndex: 1];
NSString *needle = [haystack substringWithRange:needleRange];

This one might be a bit over the top for your rather trivial case though.

Option 3:

NSString *needle = [haystack componentsSeparatedByString:@":"][1];

This one creates three temporary strings and an array while splitting.

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All snippets assume that what's searched for is actually contained in the string.