c - Sign extension query in case of short -

c - Sign extension query in case of short -

given,

unsigned short y = 0xffff;

when print

printf("%x", y);

i : 0xffff;

but when print

printf("%x", (signed short)y);

i : 0xffffffff

whole programme below:

#include <stdio.h> int main() { unsigned short y = 0xffff; unsigned short z = 0x7fff; printf("%x %x\n", y,z); printf("%x %x", (signed short)y, (signed short)z); homecoming 0; }

sign extension happens when typecast lower higher byte info type, here typecasting short signed short. in both cases sizeof((signed short)y) or sizeof((signed short)z) prints 2 bytes. short remains of 2 bytes, if sign bit 0 in case of 0x7fff. help much appreciated!

output of first printf expected. sec printf produces undefined behavior.

in c language when pass a value smaller int variadic argument, value implicitly converted type int. not possible physically pass short or char variadic argument. implicit conversion int "sign extension" takes place.

for reason, printf("%x", y); equivalent printf("%x", (int) y);. value passed printf 0xffff of type int. technically, %x format requires unsigned int argument, non-negative int value ok (unless i'm missing technicality). output 0xffff.

conversion int happens in sec case well. i.e. printf("%x", (signed short) y); equivalent printf("%x", (int) (signed short) y);. conversion of 0xffff (signed short) implementation-defined, because 0xffff apparently out of range of signed short on platform. produces negative value (-1). when converted int produces same negative value of type int (again, -1 represented 0xffffffff 32-bit int). farther behavior undefined, since passing negative int value format specifier %x, requires unsigned int argument. illegal utilize %x negative int values.

in other words, formally sec printf prints unpredictable garbage. practically above explains 0xffffffff came from.

c