The operation requested here is the opposite of the one implemented in the previous problem. This time, however, we could write a function and not a function template. The input is an std::string_view, which is a lightweight wrapper for a sequence of characters. The output is a vector of 8-bit unsigned integers. The following hexstr_to_bytes function transforms every two text characters into an unsigned char value ("A0" becomes 0xA0), puts them into an std::vector, and returns the vector:
unsigned char hexchar_to_int(char const ch){ if (ch >= '0' && ch <= '9') return ch - '0'; if (ch >= 'A' && ch <= 'F') return ch - 'A' + 10; if (ch >= 'a' && ch <= 'f') return ch - 'a' + 10; throw std::invalid_argument("Invalid ...
