CODEWITHSUNDEEP
chexoutput
user2821275
user2821275

Reputation:

C: Hexadecimal output comes out with "ffff"?

I have the following code:

#include <stdio.h>
#include <stdlib.h>

int main(){

int first = cdab3412;

int second = abcd1234;

int result1 = (second >> 16) | (first & 0xFFFF0000);
int result2 = (first << 16) | (second & 0x0000FFFF);

printf("Outputs: %x and %x.\n", result1, result2);

result2 turns out as expected an outputs: 34121234

However, result1 outputs ffffabcd. If I just leave it as (first & 0xFFFF0000) it correctly outputs cdab0000.

Why is result1 ffffabcd and not cdababcd?

Upvotes: 2

Views: 1517

Answers (2)

bara
bara

Reputation: 374

second is a signed integer. So when you shift it to the right the leftmost bit becomes a 1.

If you use unsigned int's you'll get the result you expect.

Signed vs. unsigned has always been a source of confusion, so you need to tread carefully.

Upvotes: 4

Freddie
Freddie

Reputation: 891

It's called sign extension. Set the types to unsigned int and it should work.

Upvotes: 5

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