NSScanner scan after equal sign

Question

oauth_token=requestkey&oauth_token_secret=requestsecret

How can I use NSScanner to get "requestkey" and "requestsecret". I can't seem to achieve it.

NSScanner* scanner = [NSScanner scannerWithString:string];
NSString *oauth_token = @"oauth_token=";
NSString *oauth_token_secret = @"oauth_token_secret=";
[scanner setCharactersToBeSkipped:nil];

NSString *token;
NSString *key;


while (![scanner isAtEnd]) {
    [scanner scanString:oauth_token intoString:NULL];
    [scanner scanUpToCharactersFromSet:[NSCharacterSet characterSetWithCharactersInString:@"&"] intoString:&token];
    [scanner scanUpToString:oauth_token_secret intoString:NULL];
    [scanner scanUpToString:oauth_token intoString:&key];

    NSLog(@"token%@", token);
    NSLog(@"key %@", key);

//token requestkey
//key oauth_token_secret=requestsecret

}

I can't seem to figure out why is it null. Thanks!

Answer 1

Nothing is null. So I can't speak to that.

It's actually a pretty straight forward error if you just follow the logic of your code line by line. For example:

[scanner scanString:oauth_token intoString:nil];
// The cursor is now just after the equals sign.
[scanner scanUpToCharactersFromSet:[NSCharacterSet characterSetWithCharactersInString:@"&"] intoString:&token];
// This leaves the cursor just BEFORE the &.
[scanner scanUpToString:oauth_token_secret intoString:nil];
// This leaves the cursor just BEFORE the "oauth_token_secret="
[scanner scanUpToString:oauth_token intoString:&key];
// This scans effectively the rest of the string into &key which is in fact
// "oauth_token_secret=requestsecret"

The simplest way to fix this is to use the scanString:intoString: method to advance the cursor to the end of oauth_token_secret.

[scanner scanString:oauth_token intoString:nil];
[scanner scanUpToCharactersFromSet:[NSCharacterSet characterSetWithCharactersInString:@"&"] intoString:&token];
[scanner scanUpToString:oauth_token_secret intoString:nil];
// This leaves the cursor just BEFORE the "oauth_token_secret="

// **FIX HERE**
[scanner scanString:oauth_token_secret intoString:nil];
// The cursor is now AFTER oauth_token_secret.

[scanner scanUpToString:oauth_token intoString:&key];

The log output now shows useful strings.

token:requestkey
key  :requestsecret

But, as H2CO3 said in the comments section, componentsSeparatedByString: is a much better fit for this use case.