Class Problem

no-reply@allegro.cc (moon_rabbits) — Wed, 28 Mar 2007 01:03:47 +0000

I am making a game similar to missile defence so that I can become used to Allegro and whatnot.

I wrote something up that generates a background and saves it to a bitmap, everything was going good until I added a class in a separate .cpp file.

1/********************
2 * Tank Class Header*
3 ********************/
4 
5#ifndef _TANK_H 
6#define _TANK_H
7 
8#define MAX_BULLETS 10
9#define MOVE_LEFT 0
10#define MOVE_RIGHT 1
11 
12#define TANK_W  100
13#define TANK_H  35
14 
15#define CANNON_W 25
16#define CANNON_H 50
17 
18class CTank
19{
20public:
21   CTank();
22   ~CTank();
23   
24   int x, y;  // x and y coordinate of the player
25   int health; // health of the player
26   int reload; // reload time of the player
27     
28   int score;
29     
30   BITMAP *tank, *cannon; //bitmaps to hold the tank and cannon
31   
32   void MoveTank(int dir);
33   void FireBullet();
34};
35 
36#endif

1/********************
2 * Tank Source File *
3 ********************/
4 
5#include 
6#include "tank.h"
7 
8CTank::CTank()
9/* Sets up tank object */
10{
11    x = (SCREEN_W/2);  // init player
12    y = (SCREEN_H/4);
13    health = 100;
14    reload = 0;
15    score = 0;
16    tank = create_bitmap(TANK_W, TANK_H);
17    cannon = create_bitmap(CANNON_W, CANNON_H);
18     
19    rectfill(tank, 10, 0, (TANK_W-10), TANK_H, makecol(45, 200, 60));
20    rect(tank, 10, 0, (TANK_W-10), TANK_H, makecol(60, 230, 70));
21}
22//--------------------------------------------    
23 
24CTank::~CTank()
25/* Deletes tank bmps */
26{
27    destroy_bitmap(tank);
28    destroy_bitmap(cannon);
29}
30//--------------------------------------------    
31 
32void CTank::MoveTank(int dir)
33/* Moves tank */
34{
35    if((dir == MOVE_LEFT) && (x < 0))
36      x -= 1;
37    else if((dir == MOVE_RIGHT) && ((x+TANK_W) > (SCREEN_W))
38      x += 1;
39      
40    return;
41}
42//--------------------------------------------    
43 
44void CTank::FireBullet()
45{}
46//--------------------------------------------    

That's the tank class header and .cpp file. The program compiles fine, but this error is given when it runs:

The instruction at "0x10020efc" referenced memory at "0x00000038". The memory could not be "read".

Click on OK to terminate the program
Click on CANCEL to debug the problem.

Help, please?

no-reply@allegro.cc (Jonatan Hedborg) — Wed, 28 Mar 2007 01:08:19 +0000

How do you use the class? Make sure you don't create it until you have initiated allegro. Post some more code.

no-reply@allegro.cc (moon_rabbits) — Wed, 28 Mar 2007 01:20:32 +0000

Here is the only other code I have written so far, the main.cpp file:

1/******************************
2 * Tank Defense v.0.1      *
3 * March 25 2007              *
4 * Kelly Crawford             *
5 ******************************/
6 
7#include 
8#include 
9#include "tank.h"
10 
11#define WINDOW_W 640
12#define WINDOW_H 480
13 
14#define MAX_CLOUDS 14
15#define MIN_CLOUDS 7
16 
17int SetUp()
18/* Initializes allegro and screen */
19{
20     allegro_init();
21     
22     install_keyboard();
23     install_mouse();
24     
25     set_color_depth(16);
26     
27     if(set_gfx_mode(GFX_AUTODETECT_WINDOWED, WINDOW_W, WINDOW_H, 0, 0) != 0) 
28         return 1;
29     
30     srand(time(0));
31          
32     return 0;
33}
34//--------------------------------------------    
35 
36void cloud_line(BITMAP *bmp, int x, int y, int color)
37/* Function called by DoLine() */
38{
39     putpixel(bmp, x, y, color);
40       
41     return;
42}
43//--------------------------------------------    
44 
45void MakeCloud(BITMAP *bmp)
46/* Draws a cloud to bmp */
47{
48    int height = 1 + (rand()%50);  // height of cloud
49    int width = 100 + (rand()%50);  // general width of cloud
50      
51    int x1 = (-30) + rand()%(SCREEN_W-30); 
52    int x2 = x1 + width;
53    int y =  10 + rand()%(SCREEN_H-100); // cloud coordinates
54      
55    int col = makecol(255,255,255);   // cloud color information
56      
57    for(int i = 0; i < height; i++) // loops until entire cloud is drawn
58    {
59        do_line(bmp, x1, y, x2, y, col, *cloud_line); // draw line of cloud
60        y += 1;
61        
62        if(i < (height/2)){
63          x1 -= 3 + rand()%5;
64          x2 += 3 + rand()%5;}
65        else{
66          x1 += 3 + rand()%5;
67          x2 -= 3 + rand()%5;}
68    }
69    
70    return;
71}
72//--------------------------------------------
73 
74BITMAP* GenerateSky(BITMAP *bmp)
75/* Generates a sky on bitmap pointed
76   to by bmp */
77{
78      int r = 140, g = 150, b = 225;
79      int col = makecol(r, g, b);
80      
81      
82      floodfill(bmp, SCREEN_W/2, SCREEN_H/2, col);  // fill screen w/ blue
83      
84      int clouds = (rand()%(MAX_CLOUDS-MIN_CLOUDS) + MIN_CLOUDS);
85      
86      for(int c = 0; c < clouds; c++)
87        MakeCloud(bmp);
88      
89      return bmp;
90}
91//--------------------------------------------
92 
93int main()
94{
95    CTank player;
96    
97    if(SetUp() != 0) return 1;  // setup + error checking for allegro
98    
99    BITMAP *bg_sky = create_bitmap(SCREEN_W, SCREEN_H); // create sky bitmap
100    BITMAP *buffer = create_bitmap(SCREEN_W, SCREEN_H); // create double buffer
101    
102    bg_sky = GenerateSky(bg_sky); // colour sky bitmap
103    
104    while(!key[KEY_ESC]){
105        
106        blit(bg_sky, buffer, 0, 0, 0, 0, bg_sky->w, bg_sky->h);
107    
108        blit(buffer, screen, 0, 0, 0, 0, SCREEN_W, SCREEN_H);
109    };
110    
111    destroy_bitmap(bg_sky);
112    destroy_bitmap(buffer);
113 
114    return(0);
115}END_OF_MAIN();

EDIT: The CTank class is used in the main() function only.

no-reply@allegro.cc (Matthew Dalrymple) — Wed, 28 Mar 2007 01:24:42 +0000

There is no semi-colon after END_OF_MAIN()

no-reply@allegro.cc (moon_rabbits) — Wed, 28 Mar 2007 01:26:49 +0000

I removed the semi-colon, the problem persists.

no-reply@allegro.cc (gnolam) — Wed, 28 Mar 2007 01:29:45 +0000

Jonatan nailed it. The class's constructor (and thus create_bitmap() etc) is called before Allegro is initialized.

no-reply@allegro.cc (Matthew Dalrymple) — Wed, 28 Mar 2007 01:30:07 +0000

CTank is declared before Allegro is initialized. The constructor of CTank uses allegro definitions.

edit:
Darn I was ...
http://www.mmmchicago.com/Transparent%20Red%20Beet%20by%20dick.gif

no-reply@allegro.cc (moon_rabbits) — Wed, 28 Mar 2007 01:32:15 +0000

Ah! It all makes sense now. Everything is working now, thanks everyone~

no-reply@allegro.cc (bamccaig) — Wed, 28 Mar 2007 01:33:26 +0000

NEVERMIND! (Runs away crying...) {smiley}

no-reply@allegro.cc (ImLeftFooted) — Wed, 28 Mar 2007 02:36:22 +0000

Quote:

/********************
* Tank Class Header*
********************/

#ifndef _TANK_H
#define _TANK_H

An underscore followed by an uppercase letter is undefined behavior. Adopt a new naming scheme.

no-reply@allegro.cc (Thomas Fjellstrom) — Wed, 28 Mar 2007 09:07:11 +0000

Quote:

An underscore followed by an uppercase letter is undefined behavior.

Actually, symbols and macros starting with an underscore are reserved for compiler/system use.

no-reply@allegro.cc (ImLeftFooted) — Wed, 28 Mar 2007 09:09:23 +0000

But the resulting behavior is undefined

no-reply@allegro.cc (Thomas Fjellstrom) — Wed, 28 Mar 2007 09:13:20 +0000

Its perfectly defined. Expect problems when the symbol you chose happens to be used in the compiler or system headers sometime in the future.

edit:

I used to use _FILENAMEHERE_H_

I now use FileNameHere_H_GUARD

no-reply@allegro.cc (Tobias Dammers) — Wed, 28 Mar 2007 18:40:11 +0000

Quote:

An underscore followed by an uppercase letter is undefined behavior.

No, it's definitely not. An identifier in C can start with any letter (upper- or lowercase), or an underscore, and after that, it can contain letters, underscores, and numeric digits.

Quote:

Actually, symbols and macros starting with an underscore are reserved for compiler/system use.

Double underscores. Single underscores should be fine.

Quote:

But the resulting behavior is undefined

Not at all.
If you happen to use a compiler-defined identifier for your own #defines, you will either prevent certain code from being read by the compiler, as in this example:

#ifndef __FILE__
#define __FILE__

// anything here will be ignored, because __FILE__ is always defined

#endif

...or it will produce compiler errors due to incompatible definitions for the identifier.

Neither of these constitute undefined behaviour.

no-reply@allegro.cc (Onewing) — Wed, 28 Mar 2007 20:19:02 +0000

Quote:

I used to use _FILENAMEHERE_H_

I now use FileNameHere_H_GUARD

Interesting... I've been using the top method since the beginning as that was the way I was taught. Never seen a problem...

no-reply@allegro.cc (bamccaig) — Wed, 28 Mar 2007 20:29:52 +0000

I could be wrong, but I assumed it wasn't a compiler rule, but a good practice. Like root declaring environment variables in all CAPS (or was it the other way around) in a *nix environment. I think it's only a problem if that identifier is already defined, such as _FILE_.

no-reply@allegro.cc (ImLeftFooted) — Thu, 29 Mar 2007 00:05:51 +0000

Quote:

Double underscores. Single underscores should be fine.

Single underscores followed by an uppercase letter are reserved for compiler usage.

Quote:

Its perfectly defined. Expect problems when the symbol you chose happens to be used in the compiler or system headers sometime in the future.

Technically the C++ spec does not define if you will collide or not, and when that collision occurs the results are compiler specific and therefore undefined.

I agree with you , I was just saying undefined to make my sentence more english and less codelish.

1	/********************
2	* Tank Class Header*
3	********************/
4
5	#ifndef _TANK_H
6	#define _TANK_H
7
8	#define MAX_BULLETS 10
9	#define MOVE_LEFT 0
10	#define MOVE_RIGHT 1
11
12	#define TANK_W 100
13	#define TANK_H 35
14
15	#define CANNON_W 25
16	#define CANNON_H 50
17
18	class CTank
19	{
20	public:
21	CTank();
22	~CTank();
23
24	int x, y; // x and y coordinate of the player
25	int health; // health of the player
26	int reload; // reload time of the player
27
28	int score;
29
30	BITMAP tank, cannon; //bitmaps to hold the tank and cannon
31
32	void MoveTank(int dir);
33	void FireBullet();
34	};
35
36	#endif

1	/********************
2	* Tank Source File *
3	********************/
4
5	#include
6	#include "tank.h"
7
8	CTank::CTank()
9	/* Sets up tank object */
10	{
11	x = (SCREEN_W/2); // init player
12	y = (SCREEN_H/4);
13	health = 100;
14	reload = 0;
15	score = 0;
16	tank = create_bitmap(TANK_W, TANK_H);
17	cannon = create_bitmap(CANNON_W, CANNON_H);
18
19	rectfill(tank, 10, 0, (TANK_W-10), TANK_H, makecol(45, 200, 60));
20	rect(tank, 10, 0, (TANK_W-10), TANK_H, makecol(60, 230, 70));
21	}
22	//--------------------------------------------
23
24	CTank::~CTank()
25	/* Deletes tank bmps */
26	{
27	destroy_bitmap(tank);
28	destroy_bitmap(cannon);
29	}
30	//--------------------------------------------
31
32	void CTank::MoveTank(int dir)
33	/* Moves tank */
34	{
35	if((dir == MOVE_LEFT) && (x < 0))
36	x -= 1;
37	else if((dir == MOVE_RIGHT) && ((x+TANK_W) > (SCREEN_W))
38	x += 1;
39
40	return;
41	}
42	//--------------------------------------------
43
44	void CTank::FireBullet()
45	{}
46	//--------------------------------------------

1	/******************************
2	* Tank Defense v.0.1 *
3	* March 25 2007 *
4	* Kelly Crawford *
5	******************************/
6
7	#include
8	#include
9	#include "tank.h"
10
11	#define WINDOW_W 640
12	#define WINDOW_H 480
13
14	#define MAX_CLOUDS 14
15	#define MIN_CLOUDS 7
16
17	int SetUp()
18	/* Initializes allegro and screen */
19	{
20	allegro_init();
21
22	install_keyboard();
23	install_mouse();
24
25	set_color_depth(16);
26
27	if(set_gfx_mode(GFX_AUTODETECT_WINDOWED, WINDOW_W, WINDOW_H, 0, 0) != 0)
28	return 1;
29
30	srand(time(0));
31
32	return 0;
33	}
34	//--------------------------------------------
35
36	void cloud_line(BITMAP *bmp, int x, int y, int color)
37	/* Function called by DoLine() */
38	{
39	putpixel(bmp, x, y, color);
40
41	return;
42	}
43	//--------------------------------------------
44
45	void MakeCloud(BITMAP *bmp)
46	/* Draws a cloud to bmp */
47	{
48	int height = 1 + (rand()%50); // height of cloud
49	int width = 100 + (rand()%50); // general width of cloud
50
51	int x1 = (-30) + rand()%(SCREEN_W-30);
52	int x2 = x1 + width;
53	int y = 10 + rand()%(SCREEN_H-100); // cloud coordinates
54
55	int col = makecol(255,255,255); // cloud color information
56
57	for(int i = 0; i < height; i++) // loops until entire cloud is drawn
58	{
59	do_line(bmp, x1, y, x2, y, col, *cloud_line); // draw line of cloud
60	y += 1;
61
62	if(i < (height/2)){
63	x1 -= 3 + rand()%5;
64	x2 += 3 + rand()%5;}
65	else{
66	x1 += 3 + rand()%5;
67	x2 -= 3 + rand()%5;}
68	}
69
70	return;
71	}
72	//--------------------------------------------
73
74	BITMAP* GenerateSky(BITMAP *bmp)
75	/* Generates a sky on bitmap pointed
76	to by bmp */
77	{
78	int r = 140, g = 150, b = 225;
79	int col = makecol(r, g, b);
80
81
82	floodfill(bmp, SCREEN_W/2, SCREEN_H/2, col); // fill screen w/ blue
83
84	int clouds = (rand()%(MAX_CLOUDS-MIN_CLOUDS) + MIN_CLOUDS);
85
86	for(int c = 0; c < clouds; c++)
87	MakeCloud(bmp);
88
89	return bmp;
90	}
91	//--------------------------------------------
92
93	int main()
94	{
95	CTank player;
96
97	if(SetUp() != 0) return 1; // setup + error checking for allegro
98
99	BITMAP *bg_sky = create_bitmap(SCREEN_W, SCREEN_H); // create sky bitmap
100	BITMAP *buffer = create_bitmap(SCREEN_W, SCREEN_H); // create double buffer
101
102	bg_sky = GenerateSky(bg_sky); // colour sky bitmap
103
104	while(!key[KEY_ESC]){
105
106	blit(bg_sky, buffer, 0, 0, 0, 0, bg_sky->w, bg_sky->h);
107
108	blit(buffer, screen, 0, 0, 0, 0, SCREEN_W, SCREEN_H);
109	};
110
111	destroy_bitmap(bg_sky);
112	destroy_bitmap(buffer);
113
114	return(0);
115	}END_OF_MAIN();