Solutions for slow performance?

**MrWizard** · 08-23-2002

Originally posted by Sebastiani

BTW, never do:

delete x;

Instead,

if(x) //...or if you like, if(x != NULL)
delete x;

This will ensure that you don't crash the proggie from deleting a NULL pointer...

I like to go one step further. After all of that I set the pointer to null, so if I try and access it later accidently the program will fault. I usually just make a macro for this.

Code:

#define SafeDelete( x )    if( x ) delete x, x = NULL;

**Hunter2** · 08-23-2002

Sebastiani,

You need to use an iterator thingee?? I thought that as you erased an object, the rest of them would move to fill in the gap!

...and don't delete the actual vector cells, since the STL will do that for you

fighters is a vector of pointers; FillYourBrain (in another thread) told me that you had to loop through the vector and delete each one...

Nick,

You have to
be careful with stuft like

for (int i = 0; i < 40; i++)
/* do more stuft */

for ( i = 0; i < 40; i++)
/* do more stuft */

All of your classes with virtual functions must have a
virtual destructor

Are these related?? (and why do I have to be careful with loops? slow?)

you're best off generating these ahead of time

You mean like, copy and paste that code and call it GenerateMask(), then make TransBlt() take a mask and a bitmap?

P.S. I heard from someone that you should never use i++ in for loops, as it is slower than ++i....

**Hunter2** · 08-23-2002

Wow Nick!!!! You da man! I tried the GenerateMask() thingee, and when I ran the game with the profiler, TransBlt's time-used vs. running time percentage dropped to around 7%, from a previous 25-27%

**Sebastiani** · 08-23-2002

Good job on the transblit!

As to your questions, I was assuming the code you posted was attempting to delete the entire vector. Again, in that case, you need to loop through it and delete YOUR objects. Than call a single delete on the vector. What was suspect about your code was that it seemed to delete the first cell only.

fighters.erase(&fighters[0]);

instead of

fighters.erase(&fighters[x]);

...if you catch my drift.

**Hunter2** · 08-23-2002

I'll try that later with a simpler program (i.e. one that makes a vector of ints, deletes it and quits

).

Nick · 08-23-2002

You can delete null pointers. This is valid code
char* p = 0;
delete p;
http://www.parashift.com/c++-faq-lite/

What I meant was this isn't standard c++ infact in won't compile
on just about any compiler other than visual c++ 6.0

for (int i = 0; i < 40; ++i)
continue;

for (i = 0; i < 40; ++i)
continue;

http://www.mvps.org/vcfaq/lang/1.htm

Are these related?? (and why do I have to be careful with loops? slow?)

No let's say you have a class A and B like this

Code:

class A 
{
public:
      A() { p = new int[40]; }
      ~A() { delete[] p; }
      virtual void draw();
private:
       int* p;
};

class B : public A
{
public:
        B() { q = new int[40]; }
        ~B() { delete[] q; }
        void draw();
private:
        int* q;
};

B* bp = new B;
A* ap = bp;

ap->draw;
delete ap;

Well B's draw function gets called but B's destructor
does not. Instead only A's destructor get's called. You can
try this out by writing some simple classes and have
them printout something in the destructor. This could cause
a memory leak. Other than that you need to turn up warnings
on your compile cause most compilers will warn you of this.

Indexing a vector should be as
fast an array but erasing from the middle of one is suppose to be slow. http://www.infosys.tuwien.ac.at/Rese...al/prwmain.htm looks like a good tutorial.

Most people who use visual c++ with the stl use
www.stlport.com

**SilentStrike** · 08-24-2002

Could you start the game in a rocket limit break and profile it then? That's pretty much the only situition where the game runs unacceptably slow.. so that's where you should focus the optimization efforts.

**Hunter2** · 08-24-2002

I could

Actually, that never really occured to me, but I pretty much figure it's got something to do with the rockets' movement/drawing code. Lasers, when moving, just move 12 pixels upwards, while Rockets have to calculate the direction to the alien (some trig), figure out which way to turn (some more trig), and then accelerate in that direction (some more trig). Then in the Rockets' drawing code, it has to draw both the rocket and the target

I'll try the profiler thing thoug...

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