returning three dimensional array

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Join Date: Oct 2007

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phylon

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returning three dimensional array

Nov 2nd, 2007

Hello
I am having no problem while returning 1 dimensinal array
But am having trouble with 3 dimenional array

No problem with this code

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float Mat[][][];
float Mat[];

float *funct1(void)
      {
return Mat;
}

void funct2()
        {
        float *Mat;
         Mat=funct1();
}

But this doesnt work

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float Mat[][][];

float *funct1(void)
{
Mat[][][]={........};
return Mat;
}

void funct2()
{
float *Mat;
Mat=funct1();
}

Is there anyway I can return 3 dimensional arrays ?

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Join Date: Nov 2007

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Belrog

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Re: returning three dimensional array

Nov 2nd, 2007

What are your compiler errors?

Last edited by Belrog : Nov 2nd, 2007 at 2:53 am. Reason: Grammar mistakes

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Join Date: Oct 2007

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mank

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Re: returning three dimensional array

Nov 2nd, 2007

For example

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multi_return.c: In function ‘funct1’:
multi_return.c:27: warning: return from incompatible pointer type
multi_return.c:27: warning: function returns address of local variable

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  #include <stdio.h>

 float Mat[4][4][4];

float *funct1(void)
{
float Mat[4][4][4]={
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,

1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,

1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,

1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,};
return Mat;
}

void funct2()
{
int i,j,k;
float *Mat;
Mat=funct1();

         for(k=0; k<4;k++)
         {
           for (i=0; i<4; i++)
	   {
		 for (j=0; j<4; j++)
		 {
		//    printf(" %f ", Mat[k][i][j]);
		 }
		 printf("\n");
	   }
		 printf("\n");
         }

}
         
        int main() {
        funct2();
        }

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Join Date: Oct 2007

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Duoas

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Re: returning three dimensional array

Nov 2nd, 2007

I'm sure you are getting a perfectly fine return value. Your problem is that you have not supplied any type information that the compiler can use to "know" about your array.

First, please see the Wikipedia here.

Next, please be aware that only the first dimension can be [] in C, and only when you are not actually creating data. Other dimensions must have a size. So
int Mat[][][];
is an error, as is
int Mat [][10][5];
but
void printarray( int a[][10][5], int depth );
is not.

However, int *Mat; knows nothing about how many dimensions the array has, or even if it really is an array.

If your array has variable size dimensions, then you should use a simple flat array (or pointer) and calculate things on your own:

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int *index_2d_array( int *arr, int height, int width, int y, int x ) {
  int index = (y * width) + x;
  return &(arr[ index ]);
  }

// two differently sized arrays with a "center" element
int a[5][5] = {
  { 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0 },
  { 0, 0, 7, 0, 0 },
  { 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0 }
  };
int b[3][5] = {
  { 0, 0, 0, 0, 0 },
  { 0, 0, 4, 0, 0 },
  { 0, 0, 0, 0, 0 }
  }
// a[3][4] = b[1][3]
*index_2d_array( a,   5, 5,   3, 4 ) = *index_2d_array( b,   3, 5,   1, 3 );

If your Mat object is a variable-sized array, you should create a small library of functions to handle it, and place all relevant information in a structure. For example:

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typedef struct {
  int *data;
  int width, height, depth;
  } Mat_t;

int *Mat_element( Mat_t Mat, int z, int y, int x );

Hope this helps.

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Join Date: Oct 2007

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mank

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Re: returning three dimensional array

Nov 2nd, 2007

thanks

I think this one works fine

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#include <stdio.h>

float *array(void);

float *array(void)
{
static float Mat[4][4][4]={
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,

1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,

1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,

1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,
1.2,1.3,1.4,1.5,};

return (float *) Mat; 
}


int main(void)
{
float *Mat, i;
Mat = array(); 
for (i = 0; i < 16; i++) {
printf("\n %f", *(Mat++));
}
return 0; 
}