c - strange leading "f" when print out a char -

hi guys, wrote following code:

union endian {     char a;     int  b; } test; char c;  test.b = 0xaabbccdd; c =  (char)test.a; printf("0x%x\n", c); printf("0x%x\n", test.b); printf("0x%x\n", test.a); printf("0x%x\n", (char)test.a); 

but output is:

0xffffffdd 0xaabbccdd 0xffffffdd 0xffffffdd 

i want know why there leading 0xffffff before char variable.

%x interprets argument unsigned int. integers passed variadic function promoted int, signed char values being promoted signed ints using sign extension, interpreted unsigned int %x.

you can work around casting unsigned char or uint8_t.