Hi all! Recently i have been learning Isometric tiling and today i started coding a map editor. Then a problem came to mind: How the heck do i allocate the map array dynamically? My tile structure looks like this: struct Iso_Tile { int type; // type of tile int attr; // Attributes of the tile unsigned long x; // x position of tile unsigned long y; // y position of tile } So far i have just declared the map like this: Iso_Tile map[(height of map)][(width of map)]; But how do i do this dynamically??

to dynamic allocate a n - dimensional array, n>1, the other boundaries must be constant:

eg makeing a 4x4 array, one of them must be know at "compile time"

#include "stdlib.h"

struct my
{
int i;
char x;
};

int main(int argc, char* argv[])
{
my (*cp)[4];

int screeny = 4;
cp = new my[screeny][4];

cp[2][2].i = 5;

delete [] cp;

return 0;
}

the 4 in "my (*cp)[4];" and "cp = new my[x][4];" can't be replaced by a variable.
a way around this is to use single dimension array, and calulate the index.

int main(int argc, char* argv[])
{
my *cp;

int screenx = 4, screeny = 4;
cp = new my[screenx*screeny];

int elementx = 2, elementy = 2;
cp[ elementy * screeny + elementx].i = 5;

delete [] cp;
return 0;
}

and remember to check for failed allocation ( pointer returned == NULL )

Edited by - Claus Hansen Ries on June 13, 2000 6:49:59 AM

Thanks for the help Claus!

Only one question:

Why can''t i allocate the second dimension of the array?

It is possible to have array bounds dynamic in all dimensions. The code just gets uglier.

Allocation:

typedef struct Iso_Tile * pIso_Tile;typedef pIso_Tile * ppIso_Tile;ppIso_Tile map = new pIso_Tile[height];for (int a = 0; a < height; a++) {  map[ a ] = new Iso_Tile[width];}  

Deallocation:

for (int a = 0; a < height; a++) {  delete [] (map[ a ]);}delete [] map; 

Edited by - SiCrane on June 13, 2000 10:15:20 AM

why not:


struct tile
{
int type, attr;
char blah;
};

main( )
{
tile* theWorld; // worl ptr

// dynamic allocation
// read worldwidth & worldheight from whatever source
theWorld = new tile[ worldwidth * worldheight ];

// or even:
// theWorl = (tile*) malloc( worldwidth * worldheight * sizeof(tile) );

// to access tile [40][12]
theWorld[ 40*worldwidth + 12].type = 0;

delete theWorld;
// or free( theWorld );
}


just make sure the way you access a single cell: what is the column, what is the row...

If I''m not mistake, Jehan, you must call your delete like this:

delete[] theWorld;

Otherwise it''ll just delete the first element in your array.

i have to admit, those typedef are quite a stunt =)

allocate

            Iso_Tile** myMap;myMap = new Iso_Tile[map_width];for (int i = 0; i < map_width; i++){   myMap<i>  = new Iso_Tile[map_height];}       [/source]now all you have to do to access a cell is just like you would a normal arraymyMap[width_position][height_position] = whatever;deallocate[source]for (int i=0; i<map_width; i++){   delete [] myMap[i];}delete [] myMap;                

Edited by - ncsu121978 on June 13, 2000 11:27:13 AM

If you want dynamicness, use Linked lists, otherwise, you will just obfuscate your code so bad you will have to abandon it.

-----------------------------

A wise man once said "A person with half a clue is more dangerous than a person with or without one."

A linked list for this would be overkill, and slower than molases going uphill in the middle of january. The single dimentional array is your best bet.

OneEyeLessThanNone

striving towards insanity