topic ? operator warning in CodeWarrior Development Tools

? operator warning

markulhu — Wed, 08 Apr 2015 07:45:48 GMT

signed char X1,X2,X3;

X3 = (X1 > X2)? 127: -128;

When i compile this code, the compiler display warning message said "possible lost of data".

But compile the code "X3 = (X1 > X2)? 127: -127;" is ok.

So do that "signed short" with -32768, and "signed long" with -2147483648

Why? Is this a compiler's Bug?

Re: ? operator warning

BlackNight — Wed, 08 Apr 2015 08:20:43 GMT

the compiler is a little bit over-cautious here: -128 gets promoted to int, which is 0xffff'8000 (as 16bit int), and then truncated back to signed char with the assignment.

So the compiler warns about these uppper 8bits lost (which are not really an issue).

You can get rid of that warning with a cast like this:

X3 = (signed char)((X1 > X2)? 127: -128);

Erich

Re: ? operator warning

markulhu — Thu, 09 Apr 2015 03:13:28 GMT

Thank you Erich Styger!

Today,i tring to compile code "signed long X1 = -2147483648"(0x8000 0000), the complier warning: Unary minus operator appiled to unsigned type.

just "signed long X1 = 0x80000000"is the right way?

How about your idea?