"Unsigned / int mixup (?)"

Hello.
In a struct:

Code:

---

<...>
unsigned upper : 4;
<...>

---

The above 'upper' field is populated by a int mySQL field whose value is a bit-field with 4 possible values (that stack, e.g. a row whose value is 15): 1|2|4|8. the value is introduced to the var as:

Code:

---

instance->upper = atoi(var-with-result-from-mysql);

---

I've faced this for the first time today, I didn't get why/how it works -- I thought it was broken and would leak/overflow.
Are you able to clarify this for me?
Thank you for your time.

I'm not sure what your question is. You should use unsigned int types for your bit fields. If you try to assign a bigger value, they will just be truncated. If you try to fit 16 in there, you should end up with 0 because unsigned overflow's behavior is defined in C.


Quzah.

but later in the code, the following works:

Code:

---

if( instance->upper&8 ) { <print value of upper in console> }

---

and it prints 8 (in a entry whose upper value is 8) so yeah I don't get what could be going on
Thank you for your reply.

note: I'm compiling in GCC
note2: the code is not mine; I'm actually curious to know why it behaves like that.

I'm still not sure what your actual question is. But with a four bit unsigned value, the upper bit is 8, but the upper value is 15.

8 + 4 + 2 + 1 = 15


Quzah.