getting certain portion of nsstring - ios

Question

I have string as follows in objective c
NSString *str = #"access_token=E2JmCPLtVySGn-cGGJGGnQ&email=abc#gmail.com";
How can i get only E2JmCPLtVySGn-cGGJGGnQ ?

Answer 1

You can use a Regular Expression (RegEx) to find character patterns.
The pattern matching syntax can be found in the ICU User Guide Regular Expressions
In the example the pattern is: find the first "=" and all characters up to but not including the character "&". In the pattern '(?<=access_token=)" is a look-behind assertion meaning that the "access_token=" must precede the matched text, "[^&]+" the brackets the "[]" mean a character class, the "^" al but the following character, the "+" means one or more.
NSString *str = #"access_token=E2JmCPLtVySGn-cGGJGGnQ&email=abc#gmail.com";
NSString *regexPattern = #"(?<=access_token=)[^&]+";
NSString *found = nil;
NSRange range = [str rangeOfString:regexPattern options:NSRegularExpressionSearch];
if (range.location != NSNotFound) {
found = [str substringWithRange:range];
}
NSLog(#"Range: %#", NSStringFromRange(range));
NSLog(#"found: %#", found);
NSLog output if found:
Range: {13, 22}
found: E2JmCPLtVySGn-cGGJGGnQ

Answer 2

There is a method of the NSString class called rangeOfString: that returns an NSRange struct. If you know that your returned value always has the text access_token= and also includes &email and the format is always the same, you can use this rangeOfString: method to sniff out the token.
NSRange accessTokenRange = [str rangeOfString:#"access_token="];
//this would return (0,13) for index:0, length: 13
NSRange emailRange = [str rangeOfString:#"&email="];
//this would return (34,7)
NSInteger tokenLength = ( emailRange.location + 1 ) - accessTokenRange.length;
//the point where &email begins is at index 34, but it starts at 0
//so it's actually the 35th character
//the access_token= string is 13 characters long, so 35-13 = 22
//so you know that the actual token value is 22 characters long
NSRange trueTokenRange = NSMakeRange(accessTokenRange.length,tokenLength);
NSString *tokenSubstring = [str substringWithRange:trueTokenRange];
I don't think my math is off, zero indexing can introduce off by 1 errors if you're not careful, I usually have NSLog going on each range so I can double check where I need to add or subtract 1. But essentially you'll be starting at the 14th character, which is index 13 of the string, and reading the next 22 characters.