Convert signed short with bitset

Question

I want convert string with 0 and 1 to signed short. This work, but negative numbers I have wrong values. I think, problem is converting from unsigned to signed. How can fix that? Example: 971 is 971, 425 is 425 , -122 is 3974 , -394 is 3702 , -2032 is 2064

bitset<12> b(binary);//binary is string of 0 and 1
 cout<<(signed short)b.to_ulong()<<"\n";

Answer 1

In a 16 bit signed integer, negative numbers are represented as:

1xxx xxxx xxxx xxxx

positive numbers as:

0xxx xxxx xxxx xxxx

Example:

0000 1111 1000 0110 => 3974

What you need is a 12 bit integer, where negative numbers are represented as:

.... 1xxx xxxx xxxx

Example:

.... 1111 1000 0110 => -122

You could do something like this:

#include <iostream>
#include <bitset>
#include <string>

using namespace std;

struct C {
    signed short b : 12; // 12 bit integer
};

int main() {
    string binary = "111110000110"; // 3974
    bitset<12> b(binary);

    struct C c = { static_cast<signed short>(b.to_ulong()) };

    cout << c.b << "\n"; // prints -122
}