使用NSScanner，将十六进制字符串转十进制

例子：

　 NSString * numStr = [@"0x110" substringFromIndex:2];

unsigned long long result = 0;

NSScanner *scanner = [NSScanner scannerWithString:numStr];

[scanner scanHexLongLong:&result];

NSLog(@"result - - %lld",result);

参考网址：http://blog.csdn.net/wangyanchang21/article/details/51744937