I need to understand the logic behind this cpp code

Question

I need to understand the logic behind this cpp code

int x = 25;
unsigned int g = x & 0x80000000;

how did this code read the most significant bit of in the address of x? does the reference to 0x80000000, or binary 1000 0000 0000 0000 accomplished that task, or was it something else?

c++

asked on Stack Overflow Sep 17, 2020 by

Paztypast N • edited Sep 17, 2020 by

Paztypast N

1 Answer

For char the most significant bit is typically the sign bit as per Two's Complement, so this should be:

 char x = 25;
 unsigned int msb = x & (1 << 6);

Where (1 << 6) means the 6 bit, counting from 0, or the 7th counting from 1st. It's the second-to-top bit and equivalent to 0x40.

Since 25 is 0b00011001 you won't get a bit set. You'll need a value >= 64.

answered on Stack Overflow Sep 17, 2020 by

tadman • edited Sep 17, 2020 by

tadman

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