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Why can this JNI Exception Access Violation Crash be avoided when some printf are plugged in C code?

C DLL connected with Java GUI. It runs well with some debugging printfs to DOS windows are plugged in C code while Exception Access Violation crashes when the debugging printfs are commented off. There are some pointers referred to a large size dynamic memory got from calloc().

Is JNI have some inner limit for dynamic memory referring?
When Crashes, I found the pointer to array in dynamic memory was corrupted unexplainably. When printfs are added back in, the pointers work OK.

Obviously I don't want to release the code with those printfs in the code and debugging outputs hanging over the screen.

Thanks a lot!    
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yuanzhou
Asked:
yuanzhou
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1 Solution
 
CEHJCommented:
Better post the code
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yuanzhouAuthor Commented:
So many codes and functions interrelated. I guess my description was about the essense of problem. My colleagues also encounterred similar situations and tried to explain it by " printf may change memory and put off memory corruption" but still can't fix it or work around it.
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CEHJCommented:
>>So many codes and functions interrelated.

Are there that many commented-out printf statements?
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yuanzhouAuthor Commented:
Many commented-out statements includes printf. I use VC++ 6.0 to compile the DLL.
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CEHJCommented:
Personally i'd think there's more likely to be a problem caused by a printf *not* commented out accessing something that *is*
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yuanzhouAuthor Commented:
Anything commented off is not being accessed by the remaining codes.  
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yuanzhouAuthor Commented:
In JNI, will a JAVA garbage collector corrupt the C pointer to dynamic memory of C DLL?
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bpmurrayCommented:
If commenting out stuff causes it to fail, I'd immediately suspect that you are misusing an automatic variable, most likely a string.
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yuanzhouAuthor Commented:
I just found one of the pointer reach beyond its define in the C world and corrupt another pointer though I don't quite understand why inserting printfs can put off the crash. Anyway thank you for the helpful discussion.
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bpmurrayCommented:
That's what I meant by automatic variables - when you have strings being displayed, they take up memory space, but if your pointers point to something that overflows into your printf stuff, it doesn't matter too much. When you remove your printfs, it now points into your instructions, corrupting your program and causing a crash.
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yuanzhouAuthor Commented:
You gave me a very sound reasoning. Thank you very much!
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CEHJCommented:
>>but if your pointers point to something that overflows into your printf stuff

How does/can it 'overflow'?
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yuanzhouAuthor Commented:
This was a pointer to struct array of dim 300, but the pointer incremented to 20000 to build up a large than expected array, therefore corrupted its neighoring pointer value unless printfs were inserted to keep them isolated, from the understanding I've got now.  
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