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returning three dimensional array

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returning three dimensional array

 
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  #1
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
C Syntax (Toggle Plain Text) 
  1. float Mat[][][];
  2. float Mat[];
  3.  
  4. float *funct1(void)
  5.       {
  6. return Mat;
  7. }
  8.  
  9. void funct2()
  10.         {
  11.         float *Mat;
  12.          Mat=funct1();
  13. }

But this doesnt work

C Syntax (Toggle Plain Text) 
  1. float Mat[][][];
  2.  
  3. float *funct1(void)
  4. {
  5. Mat[][][]={........};
  6. return Mat;
  7. }
  8.  
  9. void funct2()
  10. {
  11. float *Mat;
  12. Mat=funct1();
  13. }

Is there anyway I can return 3 dimensional arrays ?
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Re: returning three dimensional array

 
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  #2
Nov 2nd, 2007
What are your compiler errors?
Last edited by Belrog; Nov 2nd, 2007 at 3:53 am. Reason: Grammar mistakes
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Re: returning three dimensional array

 
0
  #3
Nov 2nd, 2007
For example

C Syntax (Toggle Plain Text) 
  1. multi_return.c: In function ‘funct1’:
  2. multi_return.c:27: warning: return from incompatible pointer type
  3. multi_return.c:27: warning: function returns address of local variable

C Syntax (Toggle Plain Text) 
  1.   #include <stdio.h>
  2.  
  3.  float Mat[4][4][4];
  4.  
  5. float *funct1(void)
  6. {
  7. float Mat[4][4][4]={
  8. 1.2,1.3,1.4,1.5,
  9. 1.2,1.3,1.4,1.5,
  10. 1.2,1.3,1.4,1.5,
  11. 1.2,1.3,1.4,1.5,
  12.  
  13. 1.2,1.3,1.4,1.5,
  14. 1.2,1.3,1.4,1.5,
  15. 1.2,1.3,1.4,1.5,
  16. 1.2,1.3,1.4,1.5,
  17.  
  18. 1.2,1.3,1.4,1.5,
  19. 1.2,1.3,1.4,1.5,
  20. 1.2,1.3,1.4,1.5,
  21. 1.2,1.3,1.4,1.5,
  22.  
  23. 1.2,1.3,1.4,1.5,
  24. 1.2,1.3,1.4,1.5,
  25. 1.2,1.3,1.4,1.5,
  26. 1.2,1.3,1.4,1.5,};
  27. return Mat;
  28. }
  29.  
  30. void funct2()
  31. {
  32. int i,j,k;
  33. float *Mat;
  34. Mat=funct1();
  35.  
  36.          for(k=0; k<4;k++)
  37.          {
  38.            for (i=0; i<4; i++)
  39. 	   {
  40. 		 for (j=0; j<4; j++)
  41. 		 {
  42. 		//    printf(" %f ", Mat[k][i][j]);
  43. 		 }
  44. 		 printf("\n");
  45. 	   }
  46. 		 printf("\n");
  47.          }
  48.  
  49. }
  50.  
  51.         int main() {
  52.         funct2();
  53.         }
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Re: returning three dimensional array

 
0
  #4
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:
C Syntax (Toggle Plain Text) 
  1. int *index_2d_array( int *arr, int height, int width, int y, int x ) {
  2.   int index = (y * width) + x;
  3.   return &(arr[ index ]);
  4.   }
  5.  
  6. // two differently sized arrays with a "center" element
  7. int a[5][5] = {
  8.   { 0, 0, 0, 0, 0 },
  9.   { 0, 0, 0, 0, 0 },
  10.   { 0, 0, 7, 0, 0 },
  11.   { 0, 0, 0, 0, 0 },
  12.   { 0, 0, 0, 0, 0 }
  13.   };
  14. int b[3][5] = {
  15.   { 0, 0, 0, 0, 0 },
  16.   { 0, 0, 4, 0, 0 },
  17.   { 0, 0, 0, 0, 0 }
  18.   }
  19. // a[3][4] = b[1][3]
  20. *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:
C Syntax (Toggle Plain Text) 
  1. typedef struct {
  2.   int *data;
  3.   int width, height, depth;
  4.   } Mat_t;
  5.  
  6. int *Mat_element( Mat_t Mat, int z, int y, int x );

Hope this helps.
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Re: returning three dimensional array

 
0
  #5
Nov 2nd, 2007
thanks

I think this one works fine

C Syntax (Toggle Plain Text) 
  1. #include <stdio.h>
  2.  
  3. float *array(void);
  4.  
  5. float *array(void)
  6. {
  7. static float Mat[4][4][4]={
  8. 1.2,1.3,1.4,1.5,
  9. 1.2,1.3,1.4,1.5,
  10. 1.2,1.3,1.4,1.5,
  11. 1.2,1.3,1.4,1.5,
  12.  
  13. 1.2,1.3,1.4,1.5,
  14. 1.2,1.3,1.4,1.5,
  15. 1.2,1.3,1.4,1.5,
  16. 1.2,1.3,1.4,1.5,
  17.  
  18. 1.2,1.3,1.4,1.5,
  19. 1.2,1.3,1.4,1.5,
  20. 1.2,1.3,1.4,1.5,
  21. 1.2,1.3,1.4,1.5,
  22.  
  23. 1.2,1.3,1.4,1.5,
  24. 1.2,1.3,1.4,1.5,
  25. 1.2,1.3,1.4,1.5,
  26. 1.2,1.3,1.4,1.5,};
  27.  
  28. return (float *) Mat; 
  29. }
  30.  
  31.  
  32. int main(void)
  33. {
  34. float *Mat, i;
  35. Mat = array(); 
  36. for (i = 0; i < 16; i++) {
  37. printf("\n %f", *(Mat++));
  38. }
  39. return 0; 
  40. }
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