Emulated 2D Array

Nope. You''ll never get past the first row. Maybe half-way into the second. You want this instead:

int compute_offset( int x, int y, int width, int height )
{
  return ( (y * width) + x ) % ( (width * height) - 1 );
}
 

On a related note, why can''t you dynamically allocate a 2D array?

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Thanks to Kylotan for the idea!

quote:

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Original post by Oluseyi
Nope. You''ll never get past the first row. Maybe half-way into the second. You want this instead:

int compute_offset( int x, int y, int width, int height )
{
  return ( (y * width) + x ) % ( (width * height) - 1 );
}
 

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Thanks, Oluseyi.

quote:

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On a related note, why can''t you dynamically allocate a 2D array?

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It won''t work.
I do the following, and it is pointed out as an error:

something = new int [xSize][ySize];
 

Maybe I''m doing something wrong...

Also, the following line is also an error:

delete [][] something;
 

For the record..I have:

int *something;
 

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ICQ #: 149510932

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You gotta do something like
int **a;
*a = new int[maxX];
for (int i=0; i a = new int[maxY];

don''t know if thats exact.... i''ve done it once before.

PaladinGLT: Precisely.

Programmer One:

type **double_array = new type *[ dimension_1 ];
for( int n = 0; n < dimension_1; ++n )
  double_array[ n ] = new type[ dimension_2 ];
 

When deleting the 2D array, apply in reverse:

for( int n = 0; n < dimension_1; ++n )
  delete [] double_array[ n ];
delete [] double_array;
 

Alternatively, use std::vector:

std::vector< std::vector< type > > double_vector;
 

Then simply use resize to set the dimensions for each of the vectors. It''s overkill for a simple rectangular grid, but it''s much preferred for more complex solutions.

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Thanks to Kylotan for the idea!

Ahhh, thanks alot!


_____________________________________________________

ICQ #: 149510932

Google - OpenGL - DirectX - Windows Guide Network - MSDN - Symantec Virus Info

"Imagination is more important than knowledge." - Albert Einstein

How much overhead are you looking at if you want to use a 2-dimensional vector in order to accomplish a dynamic 2-d array?
ie, vector< vector > ?

quote:

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Original post by krikkit
How much overhead are you looking at if you want to use a 2-dimensional vector in order to accomplish a dynamic 2-d array?
ie, vector< vector<int> > ?

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Not much really. A vector is internally very similar to a straight, dynamically-allocated array. Indexing is simply a matter of pointer offsets, and the vector performs an internal reallocation when it needs more space in order to guarantee contiguous access.

If your internal vectors ("rows") do not change size dynamically (ie are fixed) for the entire duration of their use, there is virtually zero overhead post-initialization. If the rows only grow, then you might actually have a negative overhead (ie, using vector provides benefits both at design time - you don''t have to write the reallocation code - and all changes are atomized). If your rows grow and shrink, then you don''t even want a vector. You want a list.

So there''s no reason not to use vector... I should actually do more rigid testing but I''m very lazy.

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Thanks to Kylotan for the idea!

if your worried about speed then you want to use a vector (1D array), and treat it like a 2D array. however, speed will only be increased in sequential access (not random).

btw just an fyi:

a 2d array can be linear or planar. thus both of the following allocate a 2d array. no emulation needed, heh.