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Array take values of other variables

 
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leojma



Joined: 25 Feb 2013
Posts: 6

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Array take values of other variables
PostPosted: Mon Feb 25, 2013 12:49 pm     Reply with quote
I'm programming a 16f877a.h ... and I have in my program arrays ... at some point take values of other variables and I do not know why? Someone has this happened? please help
Ttelmah



Joined: 11 Mar 2010
Posts: 19495

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PostPosted: Mon Feb 25, 2013 1:14 pm     Reply with quote
It is happening, because you are writing beyond the end of an array somewhere.
Arrays are not 'bounds checked' (the hardware does not support this). It is up to _you_ to be careful. So (for instance):
Code:


int8 chars[10]
int16 something[4];
int8 anumber=50;

void some_code(void) {
   int8 ctr;
   for (ctr=1;ctr<=10;ctr++)
      chars[ctr]=anumber;
}
//at this point 'something[0]' will probably have been overwritten

The problem here is that in C arrays are zero referenced. So chars has entries from 0 to 9. I then write to entries 1 to 10, and since (generally) variables are stored in memory in the order they are declared, chars[10], overwrites something[0].....

Common causes of problems are:
1) Forgetting arrays are zero referenced.
2) Forgetting strings need space for the terminating null.
3) Just general errors....

Best Wishes
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Mon Feb 25, 2013 1:17 pm     Reply with quote
Read these threads. See if you are doing anything mentioned in them.

variables contain bad values -
http://www.ccsinfo.com/forum/viewtopic.php?t=46536
Simple source code = Erratic behaviour -
http://www.ccsinfo.com/forum/viewtopic.php?t=41964
possible processor problem -
http://www.ccsinfo.com/forum/viewtopic.php?t=36556
Program doesn't function after meaningless changes to code -
http://www.ccsinfo.com/forum/viewtopic.php?t=31335
leojma



Joined: 25 Feb 2013
Posts: 6

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PostPosted: Mon Feb 25, 2013 8:35 pm     Reply with quote
ok thank you very much for your help problem solved! Very Happy
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