16进制字符串的转换

//将十六进制的字符串转换成NSString则可使用如下方式:
+ (NSString *)convertHexStrToString:(NSString *)str {
if (!str || [str length] == 0) {
    return nil;
}

NSMutableData *hexData = [[NSMutableData alloc] initWithCapacity:8];
NSRange range;
if ([str length] % 2 == 0) {
    range = NSMakeRange(0, 2);
} else {
    range = NSMakeRange(0, 1);
}
for (NSInteger i = range.location; i < [str length]; i += 2) {
    unsigned int anInt;
    NSString *hexCharStr = [str substringWithRange:range];
    NSScanner *scanner = [[NSScanner alloc] initWithString:hexCharStr];

    [scanner scanHexInt:&anInt];
    NSData *entity = [[NSData alloc] initWithBytes:&anInt length:1];
    [hexData appendData:entity];

    range.location += range.length;
    range.length = 2;
}
NSString *string = [[NSString alloc]initWithData:hexData encoding:NSUTF8StringEncoding];
return string;
}

//将NSString转换成十六进制的字符串则可使用如下方式:
+ (NSString *)convertStringToHexStr:(NSString *)str {
if (!str || [str length] == 0) {
    return @"";
}
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];

NSMutableString *string = [[NSMutableString alloc] initWithCapacity:[data length]];

[data enumerateByteRangesUsingBlock:^(const void *bytes, NSRange byteRange, BOOL *stop) {
    unsigned char *dataBytes = (unsigned char*)bytes;
    for (NSInteger i = 0; i < byteRange.length; i++) {
        NSString *hexStr = [NSString stringWithFormat:@"%x", (dataBytes[i]) & 0xff];
        if ([hexStr length] == 2) {
            [string appendString:hexStr];
        } else {
            [string appendFormat:@"0%@", hexStr];
        }
    }
}];

return string;
}