Convert unsigned int to signed int C

c int unsigned-integer
darksky picture darksky · Nov 29, 2011 · Viewed 134.2k times · Source

I am trying to convert 65529 from an unsigned int to a signed int. I tried doing a cast like this:

unsigned int x = 65529;
int y = (int) x;

But y is still returning 65529 when it should return -7. Why is that?

Answer

Mysticial picture Mysticial · Nov 29, 2011

It seems like you are expecting int and unsigned int to be a 16-bit integer. That's apparently not the case. Most likely, it's a 32-bit integer - which is large enough to avoid the wrap-around that you're expecting.

Note that there is no fully C-compliant way to do this because casting between signed/unsigned for values out of range is implementation-defined. But this will still work in most cases:

unsigned int x = 65529;
int y = (short) x;      //  If short is a 16-bit integer.

or alternatively:

unsigned int x = 65529;
int y = (int16_t) x;    //  This is defined in <stdint.h>

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