How to check if NSString is contains a numeric value?

Question

I have a string that is being generate from a formula, however I only want to use the string as long as all of its characters are numeric, if not that I want to do something different for instance display an error message.

I have been having a look round but am finding it hard to find anything that works along the lines of what I am wanting to do. I have looked at NSScanner but I am not sure if its checking the whole string and then I am not actually sure how to check if these characters are numeric

- (void)isNumeric:(NSString *)code{

    NSScanner *ns = [NSScanner scannerWithString:code];
    if ( [ns scanFloat:NULL] ) //what can I use instead of NULL?
    {
        NSLog(@"INSIDE IF");
    }
    else {
    NSLog(@"OUTSIDE IF");
    }
}

So after a few more hours searching I have stumbled across an implementation that dose exactly what I am looking for.

so if you are looking to check if their are any alphanumeric characters in your NSString this works here

-(bool) isNumeric:(NSString*) hexText
{

    NSNumberFormatter* numberFormatter = [[[NSNumberFormatter alloc] init] autorelease];

    NSNumber* number = [numberFormatter numberFromString:hexText];

    if (number != nil) {
        NSLog(@"%@ is numeric", hexText);
        //do some stuff here      
        return true;
    }

    NSLog(@"%@ is not numeric", hexText);
    //or do some more stuff here
    return false;
}

hope this helps.

user_1036778 · Answer

C.Johns' answer is wrong. If you use a formatter, you risk apple changing their codebase at some point and having the formatter spit out a partial result. Tom's answer is wrong too. If you use the rangeOfCharacterFromSet method and check for NSNotFound, it'll register a true if the string contains even one number. Similarly, other answers in this thread suggest using the Integer value method. That is also wrong because it will register a true if even one integer is present in the string. The OP asked for an answer that ensures the entire string is numerical. Try this:

NSCharacterSet *searchSet = [[NSCharacterSet decimalDigitCharacterSet] invertedSet];

Tom was right about this part. That step gives you the non-numerical string characters. But then we do this:

NSString *trimmedString = [string stringByTrimmingCharactersInSet:searchSet];

return (string.length == trimmedString.length);

Tom's inverted character set can TRIM a string. So we can use that trim method to test if any non numerals exist in the string by comparing their lengths.

How to check if NSString is contains a numeric value?

7 Answers