How to convert a string containing hex to native hex in C++?

Question

Programming

In an Arduino project, I needed to assemble a hexadecimal command for an external device using string concatenation. How to convert a string like "0x0104" to like -- 0x0104 (number)? I have no experience in low-level programming, so I'm wandering around.

Answer 1

Drop 0x, then loop through the line from left to right. Each character is translated into the corresponding number, let it be h. Then result = result | h; result = result << 8; and move to the next character.
Translation from character to number - 2-3 IF.

Answer 2

std::string s = "0xaabbff";
unsigned long long a = std::stoull(s, 0, 16);