The Standard specifies that hexadecimal constants like 0x8000 (larger than fits in a signed integer) are unsigned (just like octal constants), whereas decimal constants like
Yes, it can matter. If your processor has a 16-bit int
and a 32-bit long
type, 32768 has the type long
(since 32767 is the largest positive value fitting in a signed 16-bit int
), whereas 0x8000 (since it is also considered for unsigned int
) still fits in a 16-bit unsigned int
.
Now consider the following program:
int main(int argc, char *argv[])
{
volatile long long_dec = ((long)~32768);
volatile long long_hex = ((long)~0x8000);
return 0;
}
When 32768 is considered long
, the negation will invert 32 bits,
resulting in a representation 0xFFFF7FFF with type long
; the cast is
superfluous.
When 0x8000 is considered unsigned int
, the negation will invert
16 bits, resulting in a representation 0x7FFF with type unsigned int
;
the cast will then zero-extend to a long
value of 0x00007FFF.
Look at H&S5, section 2.7.1 page 24ff.
It is best to augment the constants with U
, UL
or L
as appropriate.