Problem with char array

kamax · August 2012

Hello,

In my .h file, i have a 2d char array like this:
char grid [10][10]

Everything is fine but i can't change the size like:
grid = new grid[2][7]

I need to access the "grid" from everywhere in my .m file and i know the size only in the .m file.

What can i do ?

QuantumDoja · August 2012

One idea would be to keep two variables, one for x & y, set x to 2 and y to 7 and use those instead of numbers.

LevyMast · August 2012

kamax said:
Hello,

In my .h file, i have a 2d char array like this:
char grid [10][10]

Why are you declaring global variables in your header files?
There's something wrong with that.

If you want to access C/C++ data from Objective-C, then you should put your C/C++ data into a class,
then dynamically allocate a pointer to it. Then access your data through that pointer.

Duncan C · August 2012

kamax said:
Hello,

In my .h file, i have a 2d char array like this:
char grid [10][10]

Everything is fine but i can't change the size like:
grid = new grid[2][7]

I need to access the "grid" from everywhere in my .m file and i know the size only in the .m file.

What can i do ?

Those are 2 different issues.

If you want to be able to resize a C array, you need to create it with malloc and release it with free:

char *grid;
int height = 10;
int width = 10;

malloc(grid);

Then you have to release it with free:

free(grid);

To resize, you'd have to free the old memory and malloc a new array.

Then you have to use index math to address the memory:

grid[x + y+width];

Since the above approach has a height and a width, you can expose those to the rest of your program.

Obviously it would be better if the grid was a char* property and height and width were readonly properties, and you had a grid_resize method.

LevyMast · August 2012

kamax said:
Hello,

In my .h file, i have a 2d char array like this:
char grid [10][10]

Everything is fine but i can't change the size like:
grid = new grid[2][7]

If you want to be lazy about it, declare a 2D array with a max dimensions:


#define MAX_X	10
#define MAX_Y	10
char grid [MAX_X][MAX_Y];

Then use variables to control how large you want your array:


int max_x = 5;
int max_y = 7;

Your code should work the same as before.

kamax · August 2012

Thank you for your help. I have to say Objective C is very new for me, i'm more experienced with java.

The lazy way was my first idea, just size the grid to the max and use only a part of it. This should work but i don't want to use "bad coding way".

The idea to put the grid into a class sounds better, i will look on how to do it but i suppose i should use Duncan C method to assign the grid size in this class. Looks not so easy...

Edit:
I just remember that i must think Objects. I will try to make my grid a object with methods like getValueOf[x][y] and setValueOf[x][y] (if this is possible like in java).

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