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# Strange Visual Studio Release Mode Behavior

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### #1Oammar  Members   -  Reputation: 252

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Posted 25 August 2014 - 08:58 PM

I am encountering a strange issue when attempting to build my project for release mode. It works fine in debug mode, but my Vector3D object seems to be returning garbage when I am setting one vector equal to the other.

I've been wondering if it has something to do with not having a operator=, except the default one given by the compiler, but I'm not sure. It is strange. I was also initially wondering if the compiler was executing my code out of order due to release mode compiler optimizations, but then I noticed that my Vector3D was just garbage values for some reason.

This is what I am doing:

Vector3D playerPos = mainPlayer->getObjectPosition(); // Doesn't do anything in release mode (playerPos remains as garbage)
playerPos = this->WorldToScreen(&playerPos);


All that getObjectPosition() does is:

Vector3D& GameObject::getObjectPosition()
{
return this->position;
}


Thank you for any insight you can give me on solving this issue.

### #2Oberon_Command  Crossbones+   -  Reputation: 5179

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Posted 25 August 2014 - 09:11 PM

Is it possible that mainPlayer->position hasn't actually been initialized at that point in the program? When I see an accessor appearing to spit out garbage in release but not debug, that's usually the first thing I check.

Also, how are you checking for these garbage values? If you're only seeing them in the debugger and the program is otherwise behaving as expected (or even if it isn't), that's not too unexpected. Very optimized code can make a debugger very confused.

### #3Oammar  Members   -  Reputation: 252

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Posted 25 August 2014 - 09:18 PM

I just checked, I added a std::cout statement above to check, and it is initialized to the expected result. It seems to be having issues placing the result into the Vector3D for some reason.

The problem seems to be duplicated within debug mode when I create a custom assignment operator:

Vector3D& Vector3D::operator=(const Vector3D& rhs)
{
this->set(rhs.x, rhs.y, rhs.z);
return *this;
}


If I get rid of that assignment operator it works fine in debug mode.

Here is some more code on what I am doing:

  float x = mainPlayer->getObjectPosition().x, y = mainPlayer->getObjectPosition().y, z = mainPlayer->getObjectPosition().z;
std::cout << x << " | " << y << " | " << z << std::endl;
Vector3D playerPos(x, y, z);// = mainPlayer->getObjectPosition();
std::cout << playerPos.x << " | " << playerPos.y << " | " << playerPos.z << std::endl;
Vector3D nPlayerPos = this->WorldToScreen(&playerPos);
std::cout << nPlayerPos.x << " | " << nPlayerPos.y << " | " << nPlayerPos.z << std::endl; // INVALID RESULT


I was inspecting the matrices within WorldToScreen and they appeared out of order in the release mode, however, that may have just been the compiler debug mode in release confusion.

Edited by Oammar, 25 August 2014 - 09:41 PM.

### #4Oberon_Command  Crossbones+   -  Reputation: 5179

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Posted 25 August 2014 - 09:38 PM

That looks fine to me given the context you've provided. What happens inside of set()? What are you expecting to see and what sort of "garbage values" are you seeing, exactly?

### #5Oammar  Members   -  Reputation: 252

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Posted 25 August 2014 - 10:07 PM

set() sets the x y and z component of the Vector.

void Vector3D::set(float x, float y, float z)
{
this->x = x;
this->y = y;
this->z = z;
}


The value I'm expecting to see after the WorldToScreen is: | 512 | 384 | 0, which is what I get in debug mode without the custom assignment operator, but in release mode I'm getting:
| 4.57501e+013 | 2.47714e-039 | 4.26061e+013

I can't help but wonder now if the release mode is shifting my matrices around for some reason, I'm not sure tho, I don't think they would be nor how. I'll print those out to see if they are for some reason.

Edited by Oammar, 25 August 2014 - 10:08 PM.

### #6frob  Moderators   -  Reputation: 40611

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Posted 25 August 2014 - 10:28 PM

A full rebuild might help if something is corrupt between different libraries.

I second the 'probably uninitialized' situation.

Of course, it might not be that object that is uninitialized. Something else could be uninitialized, which in turn causes something else to stomp on it.

While it is harder to diagnose, you can still use a debugger in release build. I'd go with some breakpoints when you think you initialized it (verifying it by stepping through the dissassembly window) and some memory breakpoints on the object itself to see if someone else is stomping on it.

Check out my book, Game Development with Unity, aimed at beginners who want to build fun games fast.

Also check out my personal website at bryanwagstaff.com, where I occasionally write about assorted stuff.

### #7Oammar  Members   -  Reputation: 252

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Posted 25 August 2014 - 10:36 PM

There definitely seems to be something wrong with my library when my project is accessing it. I call the WorldToScreen function in my library and get those invalid results, but if I pull out that code from within my library and execute it manually in my other project it produces the correct results.

### #8SeanMiddleditch  Crossbones+   -  Reputation: 16436

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Posted 25 August 2014 - 11:44 PM

Vector3D playerPos(x, y, z);// = mainPlayer->getObjectPosition();
std::cout << playerPos.x << " | " << playerPos.y << " | " << playerPos.z << std::endl;
Vector3D nPlayerPos = this->WorldToScreen(&playerPos);
std::cout << nPlayerPos.x << " | " << nPlayerPos.y << " | " << nPlayerPos.z << std::endl; // INVALID RESULT

This is an invalid result from WorldToScreen - and not the vector assignment itself - from what you're implying with this code. It could be the vector but from this context it appears to almost certainly be a problem in your function there. Especially with you explicitly passing a pointer to it (why?) I'm thinking you may doing some kind of illegal aliasing violation in that code.

Vector3D playerPos = mainPlayer->getObjectPosition(); // Doesn't do anything in release mode (playerPos remains as garbage)

Depending on a few things, this is probably going to invoke your copy constructor operator, not your copy assignment operator.

Vector3D& GameObject::getObjectPosition()

It's not common for get*() functions to return a non-const (lvalue) reference. Are you sure this is the behavior you want? It's not likely the cause of the bug, but depending on various overloads you have defined, it may be suspect. Prefer to return a value or a const reference and have a separate set*() function. It's common to think that a const reference is the safest choice, but check how well your compilers handle returning by value. Compilers are getting better at it and in some cases will handle return-by-value more efficiently than return-by-const-reference.

my Vector3D object

Why are you writing your own in the first place? Even on the AAA space I want to whack people who write their own (I do understand the draw - I've done it myself far more often than I should). These kinds of bugs just don't exist in well-tested third-party libraries. Plus, it's almost guaranteed that they'll be better optimized and more featureful. Math libraries are a commodity; don't write your own.

If in doubt, http://glm.g-truc.net/0.9.5/index.html is a perfectly valid choice, even if using D3D. DirectXMath is also a good choice, even if using OpenGL. vectormath works (in Bullet) and many other 3D middlewares include their own.

I can't help but wonder now if the release mode is shifting my matrices around for some reason, I'm not sure tho, I don't think they would be nor how. I'll print those out to see if they are for some reason.

This is very possible depending on what kinds of tricks you're pulling in your matrices. I've seen a lot of "fancy" math code that abuses aliasing rules and can lead to all kinds of perfectly valid but unintended output after optimization.

I've been wondering if it has something to do with not having a operator=, except the default one given by the compiler, but I'm not sure.

Rule of Zero. You _want_ to use the compiler-generated copy/move constructors/operators (and default constructor and destructor) if at all possible, since they'll be correct more often (pretty much always) than your own (easily buggy due to subtle requirements on those constructors/operators).

There's absolutely no good reason to write a custom copy operator for something like a Vector3d. Maybe you can justify a default constructor if you want to ensure that Vectors are zero-initialized. In that case you should still strongly prefer prefer NSDMI (non-static data member initializers) and a compiler-generated default constructor.

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### #9Oammar  Members   -  Reputation: 252

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Posted 26 August 2014 - 02:40 AM

Thanks for the insightful posts. It turns out the problem was definitely in the WorldToScreen function, I was returning a local variable as a reference, which I should have known not to do, but that was the problem.

I changed the function to:

Vector3D GameZone::WorldToScreen(const Vector3D& worldPos);


Vector3D& GameZone::WorldToScreen(const Vector3D& worldPos);


### #10SeanMiddleditch  Crossbones+   -  Reputation: 16436

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Posted 26 August 2014 - 12:35 PM

Thanks for the insightful posts. It turns out the problem was definitely in the WorldToScreen function, I was returning a local variable as a reference, which I should have known not to do, but that was the problem.

Get in the habit of compiling with the highest warning level and with all warnings treated as errors. Microsoft's compiler is quite capable of diagnosing this mistake for you and catching it long before it turns into a forum thread.

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### #11Norman Barrows  Crossbones+   -  Reputation: 6094

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Posted 27 August 2014 - 07:21 AM

Get in the habit of compiling with the highest warning level and with all warnings treated as errors

i actually use second highest warning level, so i don't get 5 billion "yo dude! i'm in-lining this!" warnings. inline is the only warning i get at level 5, so i just kicked it back down to level 4. really i ought to suppress the inline warning and kick it back up to level 5.

i don't treat warnings as errors. that way you can have unused variables in a routine you're writing and still see if it compiles. but in general, the code is written so it generates no warnings (except inline warnings).

and finally, i develop in release mode only. if it works in release mode, it'll work in the final version, which is all that really matters. i've experienced and heard of too many cases like this where incorrect code works in debug but not release mode. so long ago i said to heck with debug mode all together.

for debugging, i use trace variables i can assign values to and then display.  for optimization, i use hi-rez timers and the trace variables to time sections of code and display the results.

no debug mode, no debugger, no profiler.  its not the usual way of doing things, but it avoids debug vs release mode bugs. its been years since i had a bug complex enough that it even tempted me to use a debugger. and i can hook up a timer to a section of code faster than the profiler can even load! but of all the things i do, clean simple straightforward code is the #1 weapon vs bugs.

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### #12SmkViper  Members   -  Reputation: 5364

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Posted 27 August 2014 - 07:59 AM

Get in the habit of compiling with the highest warning level and with all warnings treated as errors

i actually use second highest warning level, so i don't get 5 billion "yo dude! i'm in-lining this!" warnings. inline is the only warning i get at level 5, so i just kicked it back down to level 4. really i ought to suppress the inline warning and kick it back up to level 5.

i don't treat warnings as errors. that way you can have unused variables in a routine you're writing and still see if it compiles. but in general, the code is written so it generates no warnings (except inline warnings).

and finally, i develop in release mode only. if it works in release mode, it'll work in the final version, which is all that really matters. i've experienced and heard of too many cases like this where incorrect code works in debug but not release mode. so long ago i said to heck with debug mode all together.

for debugging, i use trace variables i can assign values to and then display.  for optimization, i use hi-rez timers and the trace variables to time sections of code and display the results.

no debug mode, no debugger, no profiler.  its not the usual way of doing things, but it avoids debug vs release mode bugs. its been years since i had a bug complex enough that it even tempted me to use a debugger. and i can hook up a timer to a section of code faster than the profiler can even load! but of all the things i do, clean simple straightforward code is the #1 weapon vs bugs.

Turn on warnings as errors + highest level warnings. Like Sean pointed out, you'll catch a ton of bugs this way before you even spend the time loading up your game to see if it broke. Plus warnings as errors will prevent you from forgetting about warnings in a file that compiled - since the compiler won't re-build a file that only built with non-erroring warnings.

The only inline-related I'm aware of is some compilers will tell you they aren't inlining something you declared inline. But you probably shouldn't be declaring anything inline anyway, since it doesn't do what most people think it does (it allows ODR violations, but doesn't actually inline your code).

I don't know how you even work on anything larger then hello world without a debugger... It's so much easier to knock out almost all of your bugs in debug mode and then only concentrate on stuff that shows up in release in release.

And please, use a profiler. Sticking timers in your code not only doesn't measure what you think it does, but changes the code, thereby changing how fast it runs, how the compiler optimizes it, and either exposing or hiding threading issues and the like. Timers also can't tell you why things are slow, like repeated Load-Hit-Stores or cache misses due to algorithm design or object layout - both things a good profiler can easily show you.

Edited by SmkViper, 27 August 2014 - 08:06 AM.

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