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How do I disable initialization of static variables?

 
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don
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How do I disable initialization of static variables?
PostPosted: Mon Dec 17, 2007 10:31 pm     Reply with quote

Hi,

Immediately after main() in the LST file there are lots of CLRF instructions where static variables are being cleared. I don't need to have the static variables set to zero. Is there a way to disable this feature?

Thanks.
Ttelmah
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PostPosted: Tue Dec 18, 2007 3:55 am     Reply with quote

Different answers according to what you really need.
First, if you want the variables initialised, but not to zero, then declare them with their values. So:

static int8 fred=100;

Which will make the compiler initialise them to your required value. Given that values must be initialised somewhere, this is a good way to deal with static values.
Second, remember that any variables declared in the 'main', inherently _are_ static already (only variables in subroutines are 're-used').
Third, if you must have static variables, and want them to retain their value on a warm boot (this is great if you are using 'restart_cause', and want values to not be reinitialised), then instead use the #locate declaration for the variable, instead of the 'static'declaration. This physically forces a value to be placed at a location in memory, that _you_ chose, and C will not initialise the area concerned. The value will be static, but not initilised by the compiler. This is how I declare 'static' values on code designed to handle a watchdog restart.

Best Wishes
mskala



Joined: 06 Mar 2007
Posts: 100
Location: Massachusetts, USA

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PostPosted: Tue Dec 18, 2007 6:10 pm     Reply with quote

I can't remember how I found this out, but for static variables that are declared outside of the main or any subroutines, just omitting the word 'static' keeps the compiler from generating the code to initialize to 0.

Code:

static int8 tenthsval;  //used for holding next number to display
static int8 onesval;
static int8 tensval;
int8 minsval;
int8 tminsval;


--- Listing ---
Code:

.................... void main()
.................... {
[ ... ]
36DA:  CLRF   05
36DC:  CLRF   06
36DE:  CLRF   07
[ other variables not cleared]



--- Symbol Table ---
Code:

005     tenthsval
006     onesval
007     tensval
008     minsval
009     tminsval
Ttelmah
Guest







PostPosted: Fri Dec 21, 2007 4:50 am     Reply with quote

If you declare variables outside the 'main', they become _global_ variables. These are inherently 'static', but because they are not declared as 'static', they are not zeroed. Difference is (of course), that they are accessible from anywhere. The use of 'static' variables, is normally to have a variable in a subroutine, that is 'distinct' from those externally.
As I said, it depends what you actually 'want'... Smile

Best Wishes
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