Hi Jakub, On Mon, Oct 19, 2015, Jakub Pawlowski wrote: > On Mon, Oct 19, 2015 at 10:35 PM, Johan Hedberg <johan.hedberg@xxxxxxxxx> wrote: > > Hi Jakub, > > > > On Mon, Oct 19, 2015, Jakub Pawlowski wrote: > >> due to type promotions in C this code was failing on some platforms. > >> > >> src/device.c:2016:8: error: format specifies type 'unsigned short' but the > >> argument has type 'uint8_t' (aka 'unsigned char') [-Werror,-Wformat] > >> properties, uuid_str); > >> ^~~~~~~~~~ > >> /build/falco/usr/include/bits/stdio2.h:39:7: note: expanded from macro 'sprintf' > >> __VA_ARGS__) > >> ^ > >> --- > >> src/device.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/src/device.c b/src/device.c > >> index 0d3a655..b4e6d53 100644 > >> --- a/src/device.c > >> +++ b/src/device.c > >> @@ -2015,7 +2015,7 @@ static void store_chrc(struct gatt_db_attribute *attr, void *user_data) > >> > >> sprintf(handle, "%04hx", handle_num); > >> bt_uuid_to_string(&uuid, uuid_str, sizeof(uuid_str)); > >> - sprintf(value, GATT_CHARAC_UUID_STR ":%04hx:%02hx:%s", value_handle, > >> + sprintf(value, GATT_CHARAC_UUID_STR ":%04hx:%02x:%s", value_handle, > >> properties, uuid_str); > > > > Wouldn't the right format specifier be %hhx in this case? > > So it was compiling fine on my machine, but when it was compiling for > all possible platforms for ChromeOS those errors came up. > The very proper thing would be probably to use "PRIu8" from <inttypes.h> > but then I found good explanation: > > ""printf() is a variadic function. Its optional arguments( and only > those ) get promoted according to default argument promotions( > 6.5.2.2. p6 ). > > Since you are asking for integers, integer promotions are applied in > this case, and types you mention get promoted to int. ( and not > unsigned int because C )"" > source: http://stackoverflow.com/questions/26362386/why-is-the-format-specifier-for-uint8-t-and-uint16-t-the-same-u > > so I understand that this uint8_t will get promoted to int, and > displayed properly. > I manually tested it for 0, 127, and 255 and looks like it's > formatting just fine. It's a bit unclear from your answer: do you still get warnings/errors with %hhx or not? Looking at the warning you got: "argument has type 'uint8_t' (aka 'unsigned char')" and the printf(3): "hh A following integer conversion corresponds to a signed char or unsigned char argument" It'd still seem like %hhx shouldn't give a warning. Even though %x might work too being able to be more specific in the type specification doesn't seem like a bad thing. Johan -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
