How to use NSScanner?

Question

I've just read Apple documentation for NSScanner. I'm trying to get the integer of this string:

@"user logged (3 attempts)"

I can't find any example, how to scan within parentheses. Any ideas?

Here's the code:

NSString *logString = @"user logged (3 attempts)";
NSScanner *aScanner = [NSScanner scannerWithString:logString];

[aScanner scanInteger:anInteger];

NSLog(@"Attempts: %i", anInteger);

Covington

Answer 1

`Here is what I do to get certain values out of a string

First I have this method defined

- (NSString *)getDataBetweenFromString:(NSString *)data leftString:(NSString *)leftData rightString:(NSString *)rightData leftOffset:(NSInteger)leftPos; 
{         
    NSInteger left, right;         
    NSString *foundData;
    NSScanner *scanner=[NSScanner scannerWithString:data];                  
    [scanner scanUpToString:leftData intoString: nil];         
    left = [scanner scanLocation];         
    [scanner setScanLocation:left + leftPos];         
    [scanner scanUpToString:rightData intoString: nil];         
    right = [scanner scanLocation] + 1;         
    left += leftPos;         
    foundData = [data substringWithRange: NSMakeRange(left, (right - left) - 1)];         return foundData; 
}

Then call it.

foundData = [self getDataBetweenFromString:data leftString:@"user logged (" rightString:@"attempts)" leftOffset:13];

leftOffset is the number of characters for the left string

Could be an easier cleaner way but that was my solution.

Whirly

you don't need the leftPos. This can be found by using the [leftData length] call. However this is great for capturing data between strings dynamically. +1 – Judah

@Kalle: NULL and nil are defined exactly the same, but have different meaning. In this case nil is the correct one. #1842483 – Dyslogia

Thanks for that -- I deleted the comment in question. Yes, NULL and nil are identical. – Virtue

Answer 2

Ziltoid's solution works, but it's more code than you need.

I wouldn't bother instantiating an NSScanner for the given situation. NSCharacterSet and NSString give you all you need:

    NSString *logString = @"user logged (3 attempts)";
    NSString *digits = [logString stringByTrimmingCharactersInSet:
         [[NSCharacterSet decimalDigitCharacterSet] invertedSet]];
    NSLog(@"Attempts: %i", [digits intValue]);

or in Swift:

    let logString = "user logged (3 attempts)"
    let nonDigits = NSCharacterSet.decimalDigitCharacterSet().invertedSet
    let digits : NSString = logString.stringByTrimmingCharactersInSet(nonDigits)
    NSLog("Attempts: %i", digits.intValue)

Terryterrye

invertedSet nice! I wasn't aware of that method. I can't remember how I solved this issue before, but it surely wasn't as elegant as this. – Hemlock

Answer 3

Here is a simple solution using NSScanner (yes, @NSResponder has a really neat solution!):

NSString *logString = @"user logged (3 attempts)";
NSString *numberString;
NSScanner *scanner = [NSScanner scannerWithString:logString];
[scanner scanUpToCharactersFromSet:[NSCharacterSet decimalDigitCharacterSet] intoString:nil];
[scanner scanCharactersFromSet:[NSCharacterSet decimalDigitCharacterSet] intoString:&numberString];
NSLog(@"Attempts: %i", [numberString intValue]);

NSLog output:

Attempts: 3

Stypsis

Answer 4

NSScanner is a linear scanner. You have to scan through the stuff you don't want to get to what you do want.

You could do [aScanner scanUpToCharactersInSet:[NSCharacterSet decimalDigitCharacterSet] intoString:NULL] to jump past everything up to the number character. Then you do [aScanner scanInteger:&anInteger] to scan the character into an integer.

Roundtree

Answer 5

here is the reg-ex usage

NSString *logString = @"user logged (3 attempts)";
NSString * digits = [logString stringByMatching:@"([+\\-]?[0-9]+)" capture:1];

Kerrin