Creating a safe filename from an NSString?

Is there way to take a NSString and turn it into a safe version that can be used as a filename to save to the user Documents directory on the iPhone.

I'm currently doing something like this:

NSString *inputString = @"This is sample text which may have funny chars and spaces in.";

NSInteger len = [inputString length];        
NSString *newFilename = [[inputString substri开发者_开发技巧ngToIndex:MIN(20, len)] stringByAppendingPathExtension:@"txt"];

This currently leaves me with something like:

This is sample text .txt

Need to make sure characters that are not allowed in filenames and stripped out too.

You'll probably end up with some regex or something. Simply because it's too dangerous to use a except-filter (you may miss some illegal chars).

Therefor I'ld recommend you to use RegexKitLite (http://regexkit.sourceforge.net/RegexKitLite/), combined with the following line of code:

inputString = [inputString stringByReplacingOccurencesOfRegex:@"([^A-Za-z0-9]*)" withString:@""];

This will replace all characters except A-Z, a-z and 0-9 =)!

You can also do it the old fashioned way instead of using a regex:

NSString* SanitizeFilename(NSString* filename)
{
    NSMutableString* stripped = [NSMutableString stringWithCapacity:filename.length];
    for (int t = 0; t < filename.length; ++t)
    {
        unichar c = [filename characterAtIndex:t];

        // Only allow a-z, A-Z, 0-9, space, -
        if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') 
        ||  (c >= '0' && c <= '9') || c == ' ' || c == '-')
            [stripped appendFormat:@"%c", c];
        else
            [stripped appendString:@"_"];
    }

    // No empty spaces at the beginning or end of the path name (also no dots
    // at the end); that messes up the Windows file system.
    return [stripped stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
}

If all you really need is a safely random filename then just use SecRandomCopyBytes to the length you want and base64-encode it.