Re: [avr-gcc-list] C coding question

[Tom Deutschman]

I agree with Nigel, but yes, (!0 == 1).

Quoted from C Programming Language Reference Manual section A7.4.7
> The
> operand of the ! operator must have arithmetic type or be a pointer,
> and the result is 1 if the value of its operand compares equal to 0,
> and 0 otherwise. The type of the result is int.
>   


Try it yourself, it's the second best way to answer a question like this.

int main(void)
{
    int8_t i8;
    int i;
    uint8_t u8;
    uint16_t u16;

    i8 = (!0);    /* i8 == 0x01 */
    i = (!0);     /* i == 0x0001 */
    u8 = (!0);    /* u8 == 0x01 */
    u16 = (!0);   /* u16 == 0x0001 */
}


I have seen TRUE and FALSE defined this way before:

#if !defined( TRUE )
#define TRUE  !FALSE
#define FALSE 0
#endif  /* !TRUE */

Here are the results from Google Code Search with "#define TRUE !FALSE" search terms:
http://www.google.com/codesearch?hl=en&lr=&q=%23define+TRUE+%21FALSE&btnG=Search

Tom

On 10/6/06, Nigel Winterbottom <address@hidden> wrote:

> -----Original Message-----
> From: larry barello

> Specifically I was looking for an efficient way to encode
>
> (bSomeBool ^ (SomeBitMask & SomeVariable))
>
> to get a true/false output.

Does it have to be an _expression_ ?

If not, what's wrong with:

if (SomeBitMask & SomeVariable)
    bSomeBool = !bSomeBool;

Nigel



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Tom Deutschman
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