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c++hexunsigned-integer

how to get a signed int from an unsigned hex in C++?

I have been trying and searching for hours now but I just don't get how I can get an negative integer from an unsigned hex. I get 24 bit hex numbers and want signed integers.

(to clarify: I get an get a 24 bit number in hexadecimal. Then I read it as an integer and then I want to give it out as a signed integer.)

0xfffef1 for example should be -271 but I don't know how to get there.

Looking forward for some advice.

I have tried to invert the 24bit and then add one like you do with binary but I don't really know how to do that either.

Solution

  • Completing the 2 complement with the most significant byte should work fine:

    #include <iostream>

int main () {

    int a = 0xfffef1;
    a |= 0xff << 24;
    std::cout << a << std::endl;
}

    See the Live Demo.