char - Hex character to int in C++

Question

How can I change a hex character, not string, into a numerical value?

While typing this question, I found many answers on how to convert hex strings to values. However, none work for chars. I remember reading somewhere that this works for strings:

std::string mystr = "12345";
unsigned int myval;
std::stringstream(mystr) >> std::hex >> myval;

However, if I do mystr[x] in a loop, this code will not work. I have tried adding a new line with std::string temp = mystr[x] and changing std::stringstream(mystr) to std::stringstream(temp), but that's not working either.

So how should I do this? Currently, I'm searching through a string of the hex chars ("0123456789abcdef".find(mystr[x]);) and using the index for the value. However, since it searches, it's slow, even if it's only searching through 16 characters.

http://ideone.com/dIyD4

Answer 1

int intval = (hexchar >= 'A') ? (hexchar - 'A' + 10) : (hexchar - '0');