What does ~0 do?

问题:

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Does ~0 mean its flipping 000000000 to 1111111111?

printf("Check: %i", ~0);

The printf results to -1, which is why I am confused.
Does -1 essentially mean the same thing as 11111111111111111 bits?

回答1:

Does ~0 mean its flipping 000000000 to 1111111111?

Yes, it does.

Does -1 essentially mean the same thing as 11111111111111111 bits?

In 2s complement representation, it does.

回答2:

Does ~0 mean its flipping 000000000 to 1111111111?

Yes, that's what it means.

printf("Check: %i", ~0);

The printf results to -1, which is why I am confused.

That's because of 2's complement arithmetic, where we have conventionally accepted zero to be

000000000000

and subtracting one from it requires a "borrow" that requires a borrow, and so on, until you "roll" the entire register

111111111111

Logically, if you add "1" to that number, it will carry, and carry, and so on until it "rolls" in the opposite direction, yielding 000000000 again.

Does -1 essentially mean the same thing as 11111111111111111 bits?

Yes, as long as you are using 2's complement signed integers.

---- Edited, to include details from cincutar's now deleted post (I wish he didn't delete it) ---

To see the same memory formatted as a (unsigned) hexadecimal number, use the command

printf("Check: %x", ~0);

which will print the output

Check ffffffff

which is (for those who don't read hexadecimal well)

11111111111111111111111111111111

回答3:

It is due to the mathematical operation "two's complement". A nice video tutorial of two's complement can be found on youtube. Here's one of them :)

youtube link

回答4:

~0 == 0xFFFFFFFF

where 0xFFFFFFFF= 32 times 1 , which is -1 in 2's compliement representation

since ~ is a bitwise operation and turns zero to one in each bit:

~0b1010 == 0b0101