Question

What is the best way to convert a char array (containing bytes from a file) into an decimal representation so that it can be converted back later?

E.g “test” -> 18951210 -> “test”.

EDITED

Answer 1

It can’t be done without a bignum class, since there’s more letter combinations possible than integer combinations in an unsigned long long. (unsigned long long will hold about 7-8 characters)

If you have some sort of bignum class:

biguint string_to_biguint(const std::string& s) {
    biguint result(0);
    for(int i=0; i<s.length(); ++i) {
        result *= UCHAR_MAX;
        result += (unsigned char)s[i];
    }
    return result;
}
std::string biguint_to_string(const biguint u) {
    std::string result;
    do {
        result.append(u % UCHAR_MAX)
        u /= UCHAR_MAX;
    } while (u>0);
    return result;
}

Note: the string to uint conversion will lose leading NULLs, and the uint to string conversion will lose trailing NULLs.