How to tell through MPLAB whether a constant is defined at run time?

[deweyusa]

I am trying to figure out if various Microchip constants that were the result of a #define earlier in program execution were defined or not at run time while I'm stepping through code with a debugger. Is there an easy way to do that? Can I somehow add the constants names to the watch window or something? MPLAB doesn't seem to want to let me do that, or I'm doing it wrong.

Thanks for any help!
-Josh

 

[Nigel Goodwin]

I don't really see the point?, why would you want to check a constant? - it's 'constant' that's the idea of it.

 

[Mike - K8LH]

I don't really see the point?, why would you want to check a constant? - it's 'constant' that's the idea of it.

Not a very helpful answer Nigel. There have been plenty of times when I wanted to check the value of a constant that's derived from a formula in the define statement.

Hi Josh. You can probably use an instruction that stores the constant value in a variable to check the value. Then delete that instruction afterwards.

Cheerful regards, Mike

 

[Pommie]

I don't really see the point?, why would you want to check a constant? - it's 'constant' that's the idea of it.

You've obviously never looked at some of the Microchip code. You can spend a long time and have to look through several files to find out if a constant is defined or not. There USB code is about the worst example I've seen for this.

Mike.

 

[deweyusa]

Thanks for the help folks. Yeah, tell me about it when it comes to Microchip and their love of constants. Mike (K8LH), you're saying to transfer the constant's value to a variable, and then track the value of the variable in the watch window? I never thought of that...brilliant!

 

[Noggin]

if you want to know if it was DEFINED or not, you can do that at compile time. I do that a good bit when I'm not 100% certain that certain defines are valid inside of header files. For instance, some code might say something like:

#if USE_SHIFT_METHOD
   variable >>= 3;
#else
   variable /= 8;
#endif

What you asked was how to you tell if the define was defined at that point...

#if USE_SHIFT_METHOD
   #warning using SHIFT method
   variable >>= 3;
#else
   #warning using stupid divide :(
   variable /= 8;
#endif

Or something else you can do is

#ifdef USE_SHIFT_METHOD
   #warning using shift method
#else
   #error stupid divides! // the error directive will cause the compile to fail
#endif

I don't know if this is what you actually want to do or not, but #define's don't always have a value. For instance, if you compile in debug mode, __DEBUG is defined, but it isn't defined as anything. I don't know if you can transfer that to a variable as in variable=__DEBUG, but I do use it to do things like

General_Exception_Handler( stuff that goes here )
{
#ifdef __DEBUG
   software breakpoint assembly instruction
#endif
}

 

[3v0]

Another option is to use a real constant instead of a #define

const int ThisConstThing =  any valid compile time expression

I think I checked in C18 and it generates the same code size if not the identical code as the #define.