Convert hex string to unsigned char in C ++

Question

I want to convert a hexadecimal representation into a string into an unsigned char variable as follows:

std::stringstream ss;
uint8_t x;
ss << "1f";
ss >> std::hex >> x;  // result: x = 0x31 (=49 in decimal and ='1' as char)

Obviously, I assumed that the conversion would result in x = 0x1f (= 31 in decimal), since 0x1f is less than 0xff, which is the maximum that can be stored in an unsigned char with 8 bits. Instead, what happened was that only the first 8 bits of my string were used in the conversion.

Can someone explain to me exactly why this happened and how to fix it?

Answer 1

std::uint8_t ( , . ) unsigned char, operator>> , . - '1' x, ASCII 49. , ASCII '1' , , ; "1e" "10" "1xyz" x == 49.

, , 8 :

std::stringstream ss;
uint8_t x;
unsigned tmp;

ss << "1f";
ss >> std::hex >> tmp; 
x = tmp;                // may need static_cast<uint8_t>(tmp) to suppress
                        // compiler warnings.

( )

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