Ok, I've butchered this.

This was a silly little program I made to get a handle on classes, but I think I've really butchered some part of this, can anyone spot my mistake?

*by the by, it's not entirely finished, but certain things SHOULD work already* I'm not desiring nor asking anyone to finish it, but I've just spent like 4 hours trying to figure out why it's not working. Feel free to call me a fool, I probably did something ridiculously stupid :(

"main.cpp" FILE:

Code:

---

#include "myheaders.h"

int main (void)

{

        lchairs *program = new lchairs;
        delete program;
        return 0;

}

---

"core.h" FILE:

Code:

---

class lchairs

{

private:

        int *elechairs;
        void flagset( int &target, const int, const char *op_type );

        bool flagcheck ( int target, const int bit );
        void elecmain();

public:

        lchairs(void);
        ~lchairs(void) { delete elechairs; }

};

void lchairs::elecmain()

{

        char menuchoice;
        while ( *elechairs > 0 )

        {
       
                cout<<"\nMenu\n\n1)Rollcall\n2 Execute\n3Replacement\n4)Exit\n";
                cin>>menuchoice;
                switch ( menuchoice )

                {

                case '1':

                        {
                       
                                for ( int x = 1 ; x >=8 ; x++ )

                                {

                                        if ( flagcheck(*elechairs, x) == true)
                                               
                                        {
                               
                                                cout<<"Number "<<x<<" is alive\n\n";
                               
                                        }
                               
                                }

                        }
                                       
                break ;

                case 2:

               
               
                case 3:

               
               
                case 4:

               
               
                default:
                break;

                }

        }

}

lchairs::lchairs()

{
               
        int *elechairs = new int;

        *elechairs = 0;
       
        for ( int x = 1 ; x <=8 ; x++ )

        flagset ( *elechairs, x, "raise" );

        elecmain();
       
}


void lchairs::flagset( int &target, const int bit, const char*op_type )

{

        if (!strcmp(op_type, "lower"))

                target = target & (int)(!(pow(2, bit - 1)));
       
        else if (!strcmp(op_type, "raise"))

                target = target | (int)(pow(2, bit - 1));
       
}



bool lchairs::flagcheck ( int target, const int bit )

{

        if ((target & (int)pow(2, bit - 1)) >= 1)

                return true;
       
        else

                return false;

}

---

"myheaders.h" FILE:

Code:

---

#include <iostream.h>
#include <cmath>
#include <cstring>

#include "core.h"

---

What is the error?

It DOES compile, but it's almost like I can't effect any change in the elechairs pointer. I am almost completely sure my bit flag check works. For "lowering" a flag, I take 2 to the power of (bit - 1), reverse it with bitwise negation, making, lets say 11011111. Then that's bitwise and to lets say 11110011. The zero in the 11011111 become a little binary wrecking ball. The opposite, 00100000 with bitwise OR will pop a flag up. Of course, taken raw these will "beat dead horses" and change 0 to 0 and 1 to 1. To check and see if a bit flag is up I just take say 00100000 and bitwise & it to a value and see if it is greater than zero. I suppose I should be using unsigned ints, but I didn't explicitly set any of them knowingly to a negative number.

I don't like this constructor:

Code:

---

lchairs::lchairs()

{
               
        int *elechairs = new int;

        *elechairs = 0;
       
        for ( int x = 1 ; x <=8 ; x++ )

        flagset ( *elechairs, x, "raise" );

        elecmain();
       
}

---

For some reason it compiles for me, when it shouldn't. elechairs is already declared with class scope, and my compiler is letting it be declared again. Odd.

Anyway, I see what you're trying to do. Try this out:

Code:

---

lchairs::lchairs()

{
               
        elechairs = new int;
        *elechairs = 0;
       
        for ( int x = 1 ; x <=8 ; x++ )

        flagset (elechairs, x, "raise" );

        elecmain();
       
}

---

You should dynamically allocate, then assign to the pointer that already exists. When passing by reference you don't have to dereference. This should work for you.

My mistake, you were trying to pass a pointer through.

Code:

---

lchairs::lchairs()

{
               
        elechairs = new int;

        *elechairs = 0;
       
        for ( int x = 1 ; x <=8 ; x++ )

        flagset ( *elechairs, x, "raise" );

        elecmain();
       
}

---

Thanks for pointing that out, but it still doesn't work. I think the problem may lie in the functions I am using to actually manipulate the flags, I'll look more closely at the checking routine...

Code:

---

        for ( int x = 1 ; x >=8 ; x++ )
        {
                if ( flagcheck(*elechairs, x) == true)
                {
                        cout<<"Number "<<x<<" is alive\n\n";
                }
        }

---

Take a good look at the condition check for the for loop. It is never satisfied.

That's a Bool function that's set to return true. What's the problem?

Code:

---

for ( int x = 1 ; x >=8 ; x++ )
        {

---

Look VERY closely at that line.

:eek:

Four hours, four stinking hours I overlooked that!

Thanks Benny, your eyes are sharper than mine!

Don't mention it, I love to help. The way I found out the problem involved breakpointing and line-by-line debugging. If you have a compiler like MSVC++, you'll be able to do the same thing, otherwise, I dunno. This sort of problem is most easily solved through step-by-step debugging. Anyway, good luck with the rest of the program.

Yeah, this program isn't much, it isn't even PONG, but it does feel good to be getting it finished. It's a bad habit to leave programs undone.

EDIT: By the way, it doesn't have any memory leaks does it?

No it looks fine to me. However, there are some things that could be improved.

I think it may be better to put the bit values in an array rather than constantly using pow() to generate them. Maths functions use a lot of CPU me thinks. Maybe do the following:

Code:

---

class lchairs

{

private:

        int *elechairs;
                int bits[8];
        void flagset( int &target, const int, const char *op_type );

        bool flagcheck ( int target, const int bit );
        void elecmain();

public:

        lchairs(void);
        ~lchairs(void) { delete elechairs; }

};

lchairs::lchairs()

{
               
        elechairs = new int;

        *elechairs = 0;

                for (int i=0;i<8;i++)
                        bits[i]=pow(2,i);
       
        for ( int x = 1 ; x <=8 ; x++ )

        flagset ( *elechairs, x, "raise" );

        elecmain();
       
}

---

You see where I'm going? So, instead of using pow constantly, just refer back to the array.

Would it be better to make the array constant to boot?

EDIT: How can I convert a number grabbed via CIN from a Char number to a INT? I.E. make '1' = 1

Yes, making the array const is better, because it should never be changed. It wont however result in better performance. It's just good programming etiquette.

For converting strings to integers, google the function atoi(). You should find it relatively simple.

Is there a standard clearscreen command for console apps?

This is your standard clear screen:

Code:

---

void ClearScreen()
{
    for(int x=0 ; x<25 ; x++)
          cout << endl;              // or cout << "\n";
}

---

:)

:rolleyes: I hate console apps so much. Even clearing the screen is dodgy. My advice? Move to Win32. It's clearly better for GUI.

That's harsh bennyandthejets!

I can't think of a better environment in which to learn programming than the console. It's all very well to say Win32 is better, no one will dispute you on that, but win32 is certainly not suitable for beginners.

Agreed. I should have been more specific. Grins2Pain, stick with the console for now, it makes things a lot easier in the beginning. Eventually, you may want to move to Win32, for better aesthetics in your programs, etc.

Actually, long term, I want to learn Win32 then MFC, then DirectX. So I'll definately be cracking the books on Win32.

Tell me, can direct X simply be called fullscreen from a console app, I mean it DOES say WIN32 console app :p

Anyhow, I got a new, REALLY odd bug. The program is now pretty much perfect(in it's own, utterly sub-pong lame way), BUT I get a HUGE error when I use menu option 3 to exit. I tried to debugger but the crash is like some really bad access violation or something MAJOR screwy and the debugger can't even stomach it.

"main.cpp"

Code:

---


#include "myheaders.h"

int main (void)

{
        int how_many;
        cout<<"How many prisoners? ( 1 to 32 )\n";
        cin>>how_many;
        lchairs *program = new lchairs( how_many );
        delete program;
        return 0;

}

---

"myheaders.h"

Code:

---


#include <iostream.h>
#include <cmath>
#include <cstring>
#include <stdlib.h>

#include "core.h"

---

"core.h"

Code:

---


#define SHOW system("CLS"); display(); cout<<"\n";

class lchairs

{

private:

        unsigned int *elechairs;
        bool active;
        int priscount;
        int bits[32];
        void flagset( unsigned int &target, const int, const char *op_type );
        bool flagcheck ( unsigned int target, const int bit );
        void elecmain();
        void elecmenu( int );
        void display();

public:

        lchairs(int count = 8);
        ~lchairs(void) { delete elechairs; }

};

void lchairs::elecmain()

{

       
        active = true;
        int menuchoice;
        while ( active == true )

        {
       
                SHOW
                cout<<"\nMenu\n\n1)Execute\n2)Replacement\n3)Exit\n\n";
                cin>>menuchoice;
                elecmenu(menuchoice);

        }               
               
}

lchairs::lchairs(int count)

{
               
        (count < 1) ? (count = 1) : ((count > 32) ? (count = 32) : (NULL)) ;
        this->priscount = count;
        elechairs = new unsigned int;
        *elechairs = 0;
        for (int i=1;i<=32;i++)
   
                bits[i]=(int)pow(2,i - 1);
       
        for (int x = 1 ; x <= this->priscount ; x++ )

                flagset ( *elechairs, x, "raise" );

        elecmain();
       
}


void lchairs::flagset( unsigned int &target, const int bit, const char*op_type )

{

        if (!strcmp(op_type, "lower"))

                target = target & ~(int)(bits[bit]);
       
        else if (!strcmp(op_type, "raise"))

                target = target | (int)(bits[bit]);
       
}



bool lchairs::flagcheck ( unsigned int target, const int bit )

{

        if ((target & (int)(bits[bit])) >= 1)

                return true;
       
        else

                return false;

}

void lchairs::elecmenu ( int choice )

{

        switch ( choice )

                {

                        case 1:

                        {
                               
                                SHOW
                                cout<<"\nWho shall die?\n\n";
                                cin>>choice;
                                if ( (choice >= 1) && (choice <= this->priscount) ) flagset( *elechairs, choice, "lower" );

                        }
                       
                        break;

                        case 2:

                        {
               
                                SHOW
                                cout<<"\nWho shall be replaced?\n\n";
                                cin>>choice;
                                if ( (choice >= 1) && (choice <= this->priscount) ) flagset( *elechairs, choice, "raise" );
                       
                        }
                       
                        break;
               
                        case 3:

                        active = false;
               
                        break;
               
                        default:
                        break;

                }

}

void lchairs::display()

{
                       
                for ( int x = 1 ; x <= this->priscount ; x++ )

                {

                        if ( flagcheck(*elechairs, x) == true)
                                               
                        {
                               
                                if (x < 10) cout<<"0";
                                cout<<x<<" |OO| ";
                                if (x % 8 == 0)

                                {
                                                               
                                        cout<<"\n";
                                        for (int z = 0 ; z <= 62 ; z++ )
                                        cout<<"-";
                                        cout<<"\n";
                                                       
                                }
                                                       
                        }
                               
                else if ( flagcheck(*elechairs, x) == false)
                                               
                        {
                               
                                if (x < 10) cout<<"0";
                                cout<<x<<" |XX| ";
                                if (x % 8 == 0)
                                                       
                                {
                                                               
                                        cout<<"\n";
                                        for (int z = 0 ; z <= 62 ; z++ )
                                        cout<<"-";
                                        cout<<"\n";
                                                       
                                }
                                                       
                        }
                               
                }

}

---

Hmmm. I've narrowed the problem down to main.cpp, where you delete the lchairs. It doesn't seem to like that. I just can't work out why. I'll work it out eventually, don't worry.

Got it! I found it while mulling over something you did. When you filled the bits array, you filled from bits[1] to bits[32]. You should have done it the way I did, filling from bits[0] to bits[31], which is the norm. What you did was muck around with some memory that wasn't yours. Declaring an array bits[32] lets you manipulate any memory from bits[0] to bits[31]. By changing bits[32], you messed around with some important system memory, or something. So, here is the fix:

Code:

---

class lchairs

{

private:

        unsigned int *elechairs;
        bool active;
        int priscount;
        int bits[33]; //<-----------fixed this
        void flagset( unsigned int &target, const int, const char *op_type );

---

It works fine with that code. Note that you're wasting 4 bytes of memory by not using bits[0]. In the future, try to implement zero-based arrays, because that's the way it's done in C++.

The reason, if you really want to know, is because the square brackets work by offsetting a memory address by the number specified. So, bits[0] offsets it zero, ie, no offset, bits[1] offsets it 4 bytes (the length of an int). This way, you always have to start from bits[0], and your final element is bits[size-1].

:rolleyes: In the future I'll remember that. I'd almost pay to know exactly what I managed to target by accident. Almost makes me want to make a program that addresses random memory locations with random values in a big loop.... almost :p

:o *yawn* Well, I've been up all night brushing up on classes, so I'm going to take a nap. I looked ahead into the next section, overloading. It seems quite useful, but it has to be the weirdest damn thing I've seen so far. I mean, overloading the unassuming little + is a little extreme lol. But I can see how for classes, it would be VERY useful. If I understand correctly, you can do... unnatural things with classes and basic math operators. Why, I think I'll overload my + sign to append arrays together as soon as I get some sleep :D

Your program would crash after the first iteration of the loop. When you crash because you access memory you don't own, it's not because you accessed that memory, it's because the OS STOPPED you from accessing that memory.
The memory you're attempting to access probably doesn't contain anything, but that's beside the point as far as the OS is concerned. I'm pretty sure, anyway.

Minor point in passing, you can combine these:

elechairs = new unsigned int;
*elechairs = 0;

like this:

elechairs = new unsigned int(0);

Quote:

---

Originally posted by HybridM
Your program would crash after the first iteration of the loop. When you crash because you access memory you don't own, it's not because you accessed that memory, it's because the OS STOPPED you from accessing that memory.
The memory you're attempting to access probably doesn't contain anything, but that's beside the point as far as the OS is concerned. I'm pretty sure, anyway.

---

Did you try the code HybridM? It didn't crash until delete was called on the lchairs object. Clearly, the compiler/OS doesn't flag this particular access violation. The four bytes at bits[32] must not be special enough to flag an immediate error, but they ARE special enough to prevent deletion of the object.

Grins2Pain, have fun with overloading, it's great.

Benny, Hybrid was talking about my joke program, the random value setter.

Hey, I got a question for you and hybrid. I'm interested in getting started with 2D directdraw and direct sound. What should I learn from here? I assume I need to know Win32 and possibly MFC. I know directdraw hasn't been updated in a while, but I can use it still right?

Please, point me in the right direction.

Well, I haven't used DirectX, only OpenGL, so I'm not sure. Go to the game programming forum, and check the sticky at the top. It contains links to just about any game/graphics site you'll ever need. Before you do however, it may help to learn some Win32 API. You have to know how to open up a window and handle messages before you can use Windows graphics. You won't need to know MFC. Nobody does IMO:p.

I think this site (theForger's) is a good place to start for Win32 API.

Good luck!

All new versions of DX support all previous versions, but a while back Direct3D kinda absorbed DirectDraw, I think DX7.

I don't know if you can still use DirectDraw methods in dx9, you may have to use an older SDK.