iOS生成一个32位的UUID

- (NSString *)uuidString

{

CFUUIDRef uuid_ref = CFUUIDCreate(NULL);

CFStringRef uuid_string_ref= CFUUIDCreateString(NULL, uuid_ref);

NSString *uuid = [NSString stringWithString:(__bridge NSString *)uuid_string_ref];

CFRelease(uuid_ref);

CFRelease(uuid_string_ref);

return [uuid lowercaseString];

}