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Converting from float[][] to float**

Started by Anfernius Mar 11, 2003 at 9:13 AM 5 replies 600+ views

Original Post

Mar 11, 2003 at 9:13 AM

Hi, I would like to know how can i put the following code to work: float a[3][3]; float **b; b = a; // doesn''t work b = (float**) a; // Looses the pointer and i''m trying to do this without using malloc to initialize ''a''. Thanks for your atention.

niyaw

Mar 11, 2003 at 9:16 AM

there''s only one o in loses.

you can''t. a two-dimensional array of floats and an array of pointers to arrays of floats have different memory layouts and can''t be casted to one another.

CpMan

Mar 11, 2003 at 11:17 AM

Just going off the top of my head here.

float* g = &a[x]; sets pointer to first array element of a[x]

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fizban75

Mar 11, 2003 at 11:18 AM

float *b = &a[0][0];

This will give you a pointer to the first element in the array. Does that give you what you want?

cgoat

Mar 11, 2003 at 11:25 AM

float [2][3] is actually one contiguous block of 6 floats, so you can only cast it to a float*. Then you lookup a specific X,Y position like so:

  
const int width = 10;
const int height = 10;

float getindex(float* parray, int x, int y)
{
return parray[y*width + x];
}

float arraytest[width][height];
getindex(arraytest, 1, 1);

TerranFury

Mar 11, 2003 at 3:32 PM

What about creating an array of float pointers, with each pointer pointing to the beginning of another column in the array, and passing that? (Yeah, it''s ugly. Yeah, you shouldn''t do it. But can you?)

niyaw

Mar 12, 2003 at 6:56 AM

yes you can.

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