比较两个C ++十六进制字符串

Question

If I have two std::strings which contain a hex value of arbitrary length, how can I compare to the two to see which one is larger in terms of value? Ideally I would like to avoid having to use a big number library.

I would like to do something like:

if(hex1 > hex2)
{
    //Do something
}

Answer 1

You can do string comparison on these numbers but there are several potential problems which would have to be accounted for:

1. A sign character ("+0X2A" will be ordered before "0X0D")
2. The existence of a "0X" ("0X2A" will be ordered before "0D")
3. The capitalization of the "0X" ("0X2A" will be ordered before "0x0D")
4. The capitalization of hex digits ("0X0D" will be ordered before "0X0a")
5. The zero padding of numbers ("0X002A" will be ordered before "0X0D")

Consideration for all these conditions and their potential combinations will be a real headache. C++11 introduced the type unsigned long long int which is at least a 64-bit unsigned integer. That gives you a whopping 16 hex characters worth of input, if your input is longer than that this won't work and you will have to parse the string.

if(stoll(hex1, 0, 16) > stoll(hex2, 0, 16)

Answer 2

Start by trimming leading zeroes.

If they are not equal length, then the longer one is greater.

If they are equal length, then loop through them from the beginning and compare each digit. Whichever string first has a larger digit in the same location as the other is greater. If you get to the end and all digits are equal, then the values are equal.

Answer 3

If you are using std::string . Works for ASCII encoding.

bool hex_greater(std::string &first, std::string &second)
{
    /* Comprasions based on size */
    int firstSize = first.size(); 
    int secondSize = second.size();
    if(firstSize > secondSize)
        return true;
    else if(firstSize < secondSize)
        return false;

    /* Convert to lower case, for case insentitive comprasion */
    std::transform(first.begin(), first.end(), first.begin(), ::tolower);
    std::transform(second.begin(), second.end(), second.begin(), ::tolower);

    /* Call the std::string operator>(...) which compare strings lexicographically */
    if(first > second)
        return true;

    /* In other cases first hex string is not greater */
    return false;
}