ios - NSString stringWithFormat added "ffffff" -

i'm trying bytes nsdata , put in nsstring. while doing "ffffff" added simultaneously :

char *array = (char *)[deviceinfo bytes]; return [nsstring stringwithformat:@"%02x:%02x:%02x:%02x:%02x:%02x", array[5],array[4],array[3],array[2],array[1],array[0]]; 

returns "53:ffffffcb:ffffffb8:51:09:fffffff0"

the issue relates sign extension compiler promotes signed char unsigned int. numbers fffff negative. %x format expects unsigned int argument.

declaring array correctly fix issue:

const uint8_t *array = [deviceinfo bytes];