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Strange bug in Release mode


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#1 belfegor   Crossbones+   -  Reputation: 2126

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Posted 31 December 2012 - 01:00 PM

I am using VS2012. I have a bug in my code that i don't know how to overcome as it appears in bizarre situation. It works fine in Debug but crashes in Release mode.

 

I have  a class with couple of vectors and some pointers:

class Foo
{
private:
    Bla*                       pBla;
 
     std::vector<shared_ptr<Node>> vBar1;
     std::vector<shared_ptr<Node>> vBar2;
     std::vector<shared_ptr<Node>> vBar3;
     //std::vector<shared_ptr<Node>> vBar4;
... more data
public:
...
};

 

When i introduced one more vector (vBar4) to this class it crashes my app even if don't use it anywhere, if i comment it then everything works.

 

WTF is going on?

 

Thank you for your time.



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#2 Khatharr   Crossbones+   -  Reputation: 2614

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Posted 31 December 2012 - 01:43 PM

Lines 10 and 12 are not valid C++ syntax.

 

[/sarcasm]

 

We need to see code before we can try to debug it.


void hurrrrrrrr() {__asm sub [ebp+4],5;}

There are ten kinds of people in this world: those who understand binary and those who don't.

#3 belfegor   Crossbones+   -  Reputation: 2126

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Posted 31 December 2012 - 01:48 PM

We need to see code before we can try to debug it.

 

I think there is no need for more code because even if i just add vector declaration (and nothing else) it just crashes my app in Release build, comment it and everything works.



#4 Sollum   Members   -  Reputation: 563

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Posted 31 December 2012 - 02:01 PM

I haven't used C++ on VS2012, only C#, but maybe solutions are handled the same way.

Are you using two or more projects in your solution, where one project contains node and the other one, the code your showing? If yes, check compilation options for those projects.

I recently had the same issue at work. Two projects set to "Any CPU" mode and one goes for "x86". Switching it to "Any CPU" didn't help either, so i usually switch all projects to x84 and make sure they are built on compilation

Edited by Sollum, 31 December 2012 - 02:02 PM.


#5 simast   Members   -  Reputation: 119

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Posted 31 December 2012 - 02:01 PM

I think there is no need for more code because even if i just add vector declaration (and nothing else) it just crashes my app in Release build, comment it and everything works.

 

I have recently seen some weird things happen when I use templates in VS2012. Have your tried to "Clean" up the .obj files and do a full rebuild of the project?



#6 fastcall22   Crossbones+   -  Reputation: 2981

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Posted 31 December 2012 - 02:07 PM

When i introduced one more vector (vBar4) to this class it crashes my app even if don't use it anywhere, if i comment it then everything works.

WTF is going on?
Memory corruption is your best bet.

Try compiling your release mode with debugging symbols, and examine where the application crashes in release mode.

EDIT:
As simast suggested, try rebuilding your project before assuming memory corruption.

Edited by fastcall22, 31 December 2012 - 02:08 PM.


#7 belfegor   Crossbones+   -  Reputation: 2126

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Posted 31 December 2012 - 02:10 PM

"Clean" then "Rebuild" and now it works. WTF???



#8 Cornstalks   Crossbones+   -  Reputation: 6882

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Posted 31 December 2012 - 02:49 PM

"Clean" then "Rebuild" and now it works. WTF???

Here's what could have happened (this happens from time to time):

 

Multiple source (.cpp) files are individually compiled into object files (.obj, or .o). Then the linker comes along and links all these object files together and creates one big executable (.exe) out of them. Compiling and linking are two different tasks, but both can be time consuming, especially in large projects. In order to cut down the time you have to wait, the compiler will first compile all .cpp files into .obj files, and then when you change a source file and rebuild, it will only rebuild that one file that was changed (why waste time rebuilding files that haven't changed?).

 

This is where the problem typically comes in. In order for the compiler to do this properly, it must build a dependency graph so it knows which source files depend on which header files (so that if you change a header file, all the source files that use it can be recompiled). It's possible for the compiler to miss a dependency for some reason, or if you change two source files, the compiler doesn't realize one has changed (could be timestamp issues or something), and now the compiler only recompiles some of the source files it should have. Now you have a problem, because some object files are up to date, and some are old and didn't get updated like they should have. The linker has no clue, though, and links them all together into an executable for you. This can lead to weird things, from crashes, to garbage computations, to pretty much anything.

 

For example, if you have a struct in a header file that has some member int x;, and you remove the x member variable from the struct because you no longer need it, and two different source files use that struct but only one gets rebuilt by the compiler, each compiled object file will have a different memory representation and layout of that struct. Now it's just a disaster waiting to happen.

 

This doesn't happen a lot, but it happens enough that you should try rebuilding before declaring nuclear war on your code base.


Edited by Cornstalks, 31 December 2012 - 02:51 PM.

[ I was ninja'd 71 times before I stopped counting a long time ago ] [ f.k.a. MikeTacular ] [ My Blog ] [ SWFer: Gaplessly looped MP3s in your Flash games ]

#9 Dunge   Members   -  Reputation: 405

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Posted 31 December 2012 - 03:31 PM

I'm not 100% certain, but maybe the clean/rebuild just moved the memory around and hid the bug, but did not fix it. I would take a look at every place you use the pBla variable. Make sure it's initialized at null, set back to null when deleted and always check for != null before using it. Also check static array before/after the places where you use your Foo class, because it might be a buffer overflow, it cause this kind of problems.



#10 Khatharr   Crossbones+   -  Reputation: 2614

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Posted 31 December 2012 - 05:07 PM

I'm not 100% certain, but maybe the clean/rebuild just moved the memory around and hid the bug, but did not fix it. I would take a look at every place you use the pBla variable. Make sure it's initialized at null, set back to null when deleted and always check for != null before using it. Also check static array before/after the places where you use your Foo class, because it might be a buffer overflow, it cause this kind of problems.

 

Yup.

 

If it wasn't just a build error.

 

Adding a vector is not a bug unless you type it in wrong, but it can cause an existing bug to crash the program or give you heisenbergs.


void hurrrrrrrr() {__asm sub [ebp+4],5;}

There are ten kinds of people in this world: those who understand binary and those who don't.

#11 Xirion   Members   -  Reputation: 213

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Posted 31 December 2012 - 05:47 PM

If i'm not mistaken, i believe it's actually because you don't use the vector.

Being in release mode you are not permitted to declare variables/methods without actually using them.



#12 Cornstalks   Crossbones+   -  Reputation: 6882

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Posted 31 December 2012 - 05:49 PM

If i'm not mistaken, i believe it's actually because you don't use the vector.

Being in release mode you are not permitted to declare variables/methods without actually using them.

That's just... wrong. You're absolutely allowed to have variables and methods that you never use. The compiler is free to remove them (to some degree), but merely having them itself is not an error in any way.


[ I was ninja'd 71 times before I stopped counting a long time ago ] [ f.k.a. MikeTacular ] [ My Blog ] [ SWFer: Gaplessly looped MP3s in your Flash games ]

#13 Bacterius   Crossbones+   -  Reputation: 7005

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Posted 31 December 2012 - 07:22 PM

If i'm not mistaken, i believe it's actually because you don't use the vector.

Being in release mode you are not permitted to declare variables/methods without actually using them.

That's just... wrong. You're absolutely allowed to have variables and methods that you never use. The compiler is free to remove them (to some degree), but merely having them itself is not an error in any way.

In most languages, at least. In Go, for instance, declaring unused variables is an error. But for C++, you can of course declare placeholder variables which you aren't actually using yet, the compiler will simply ignore them (usually). At least with correct code, adding extra unused variables should not change the program's observable behaviour.


"The best comment is a deleted comment."


#14 Ameise   Members   -  Reputation: 646

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Posted 02 January 2013 - 10:48 AM

If i'm not mistaken, i believe it's actually because you don't use the vector.

Being in release mode you are not permitted to declare variables/methods without actually using them.

That's just... wrong. You're absolutely allowed to have variables and methods that you never use. The compiler is free to remove them (to some degree), but merely having them itself is not an error in any way.

In most languages, at least. In Go, for instance, declaring unused variables is an error. But for C++, you can of course declare placeholder variables which you aren't actually using yet, the compiler will simply ignore them (usually). At least with correct code, adding extra unused variables should not change the program's observable behaviour.

 

So long as their construction/destruction has no global side-effects.


Edited by Ameise, 02 January 2013 - 10:49 AM.


#15 Aliii   Members   -  Reputation: 1112

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Posted 03 January 2013 - 05:32 AM

The last time Ive had a bug like this it was becasuse the debug mode did additional things like initializing variables to NULL. ....in debug mode everything was fine but in "normal" mode it produced a weird error.



#16 NewDisplayName   Members   -  Reputation: 351

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Posted 03 January 2013 - 10:48 AM

Clean and Rebuild may have worked because the dependent library, that is associated with the class, might be built previously in debug mode, and since you just switched to Release and rebuilt, it might not have been picked up appropriately. For Release builds, all the dependencies should also be built in release mode, otherwise it won't work.






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