NSString extension to generate a random alphanumeric string of length n.

RandomStringWithLength.m

/* Created by Hersh Bhargava of H2 Micro (www.h2micro.com) */

@interface NSString (Randomize)
+ (NSString *)randomStringWithLength:(int)length;
@end

@implementation NSString (Randomize)

+ (NSString *)randomStringWithLength:(int)length
{
    NSString *alphabet  = @"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXZY0123456789";
    NSMutableString *s = [NSMutableString stringWithCapacity:length];
    for (NSUInteger i = 0U; i < length; i++) {
        u_int32_t r = arc4random() % [alphabet length];
        unichar c = [alphabet characterAtIndex:r];
        [s appendFormat:@"%C", c];
    }
    return s;
}

@end