Back to For Beginners

Problems with pointers to arrays of objects.

For Beginners

Started by Radagar October 02, 2002 10:41 AM

13 comments, last by Radagar 21 years, 6 months ago

Radagar

148

Author

October 02, 2002 10:41 AM

Okay, I have a CTile class holding some info about a map position. I''m declaring the Map as CTile Map[10][10]. Now, I want to pass a pointer to this structure to a function that will draw the map. I can''t get this to work! See my code below, I know I''m doing it wrong, (CMap ** != CMap[10][10]) but, I don''t know how to do it right. Any help would be appreciated.

  
define USE_CONSOLE
#include <allegro.h>

class CTile
{
public:
    BITMAP        *tile_base;
    BITMAP        *tile_terrain;
    bool        passable;
};

PALETTE        palette;
BITMAP        *buffer;
BITMAP        *tile_base_water;
BITMAP        *tile_base_grass;
BITMAP        *tile_terrain_tree;

void draw_map(CTile** pMap);

int main()
{
    allegro_init();
    install_keyboard();

    set_color_depth(16);
    set_gfx_mode(GFX_AUTODETECT, 640, 480, 0, 0);

    //setup Bitmaps

    buffer = create_bitmap(SCREEN_W, SCREEN_H);
    tile_base_water = load_bitmap("water.bmp", palette);
    tile_base_grass = load_bitmap("grass.bmp", palette);
    tile_terrain_tree = load_bitmap("tree.bmp", palette);

    //Create Map

    CTile Map[10][10];

    for (int x = 0; x < 10; x++)
    {
        for (int y = 0; y < 10; y++)
        {
            Map[x][y].passable = true;
            Map[x][y].tile_base = tile_base_grass;
            Map[x][y].tile_terrain = NULL;
        }
    }
    Map[2][5].tile_terrain = tile_terrain_tree;
    //End Map Creation


    while (! key[KEY_ESC] )
    {
        draw_map(Map);
    }
    //Destroy Bitmaps & exit

    destroy_bitmap(buffer);
    destroy_bitmap(tile_base_water);
    destroy_bitmap(tile_base_grass);
    destroy_bitmap(tile_terrain_tree);
    return 0;
}

void draw_map(CTile** pMap)
{
// ...

}

Oh, and the error I''m getting if you need it, is


error C2664: ''draw_map'' : cannot convert parameter 1 from ''class CTile [10][10]'' to ''class CTile ** ''
        Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
Error executing cl.exe.

Thanks! ~~~~~~~~~~~ Chris Vogel ~~~~~~~~~~~

WyrmSlayer RPG - In Early Development

Arek the Absolute

350

October 02, 2002 04:45 PM

I have to say the easiest way would probably be to use a 1 dimensional array instead of 2. If you do this:

CTile Map[100];

You''ll be able to pass a (CTile* pMap) to your function, and bypass your entire problem.

-Arek the Absolute

-Arek the Absolute"The full quartet is pirates, ninjas, zombies, and robots. Create a game which involves all four, and you risk being blinded by the sheer level of coolness involved." - Superpig

Radagar

148

Author

October 02, 2002 05:03 PM

I really prefer to keep the multi-dimensional array.

I got around my problem by creating a CMap class that holds the CTile array, then just passing a pointer to the map class to the function to draw the screen.

~~~~~~~~~~~
Chris Vogel
~~~~~~~~~~~

WyrmSlayer RPG - In Early Development

Glass_Knife

8,637

October 02, 2002 05:28 PM

To pass an array to a function, you can do this:
Prototype: void drawMap(CTile pMap[]);
Function call: drawMap(pMap);

The complier does not need to know the size of the array...
but that's for a 1d array, for a 2d array, it need to know the size of the 2nd dimension.

Prototype: void drawMap(CTile pMap[][10]);
Function call: drawMap(pMap);

    #include <iostream.h>class FOO{	int x, y;};void drawIt(FOO pMap[][10]);int main(){	FOO array[10][10];	drawIt(array);	return 0;}void drawIt(FOO pMap[][10]){	cout << " in drawIt" << endl;}

hope this helps...

I think, therfore I am.
I think?

[edited by - glass_knife on October 2, 2002 6:29:54 PM]

I think, therefore I am. I think? - "George Carlin"
My Website: Indie Game Programming

My Twitter: https://twitter.com/indieprogram

My Book: http://amzn.com/1305076532

Anonymous

October 03, 2002 11:31 AM

In addition:

TypeX array[x]; TypeX **array2; ''array'' is a constant pointer, where ''array2'' is not. You could also declare you variable as TypeX** and allocate: array2 = new TypeX*[10]; for( int i=0; i<10; i++ ){ array2 = new TypeX[10]; } Now, you can send it to ''func( TypeX** v )'' There may be faster/more efficient ways, but this works. I (like Glass_Knife) hopes this helps. <img src="wink.gif" width=15 height=15 align=middle> —- — — – – – – – - - – - please don''t hesitate to correct any errors. :D —-

Anonymous

October 03, 2002 11:35 AM

Oops... Sorry, I found a mistake in my code, heh.

The mistake is in the for loop:

array2 = new TypeX[10];

should be:

array2 = new TypeX[10];

:D ~ z ~ :D

Hairu

122

October 03, 2002 11:40 AM

It''s simple really. Arrays are pointers just tell the function to use it as a pointer by using the address-of operator like this.

CTile Map[10][10];
void draw_map( CTile** );

..... blah blah blah
....

draw_map( &Map );

Anonymous

October 03, 2002 11:50 AM

doesn''t (seem to) work. (use the post before that, or f( ctile x[][10]))

To clean up the allocated array (from my previous code), delete
all ''sub'' arrays first:

for( int i=0; i<0; i++ ){
delete [] array2;
}

delete [] array2;

:D ~z~ :D

Anonymous

October 03, 2002 11:55 AM

Again! An error.. I need to be hit. heh.

Loop is this:

for( int q=0; q<0; q++ ){
delete [] array2[q];
}

hrm... italics.

Hairu

122

October 03, 2002 12:09 PM

This is not correct

Again! An error.. I need to be hit. heh.

// BEGIN BLOCK
Loop is this:

for( int q=0; q<0; q++ ){
delete [] array2[q];
}

hrm... italics.

// END BLOCK

the loop is never accessed, you set q to 0, and then test that it''s less than it.. it''ll never evaluate to true

Problems with pointers to arrays of objects.

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Problems with pointers to arrays of objects.

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines