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Declaration of array

Posted on 1998-08-21
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Last Modified: 2010-04-15
I have been declaring my array in the fashion shown in the code segment below and the max size for my PC is 64x64. What's wrong with my codes? How can I increase the sizes of the arrays to 512x512? Do I have to deal with setting the buffer size or virtual memory?

My declaration of array is as follow:

#define HEIGHT 32
#define WIDTH 32

short  x,y,ro[HEIGHT][WIDTH],go[HEIGHT][WIDTH],bo[HEIGHT][WIDTH];
short  rq[HEIGHT][WIDTH],gq[HEIGHT][WIDTH],bq[HEIGHT][WIDTH];
float  rn[HEIGHT][WIDTH],gn[HEIGHT][WIDTH],bn[HEIGHT][WIDTH];
float  rq2[HEIGHT][WIDTH],gq2[HEIGHT][WIDTH],bq2[HEIGHT][WIDTH];


The way I use the array :

  for (x=0;x<HEIGHT;x++)
     {
       for (y=0;y<WIDTH;y++)
          {
              Infile>>ro[x][y]>>go[x][y]>>bo[x][y];

              rn[x][y]=ro[x][y]/255.0;
              gn[x][y]=go[x][y]/255.0;
              bn[x][y]=bo[x][y]/255.0;

              rq[x][y]=ro[x][y]*15/255;
              gq[x][y]=go[x][y]*15/255;
              bq[x][y]=bo[x][y]*15/255;

              rq2[x][y]=rq[x][y]/15.0;
              gq2[x][y]=gq[x][y]/15.0;
            bq2[x][y]=bq[x][y]/15.0;

       }
  }

Can I have an example of more efficient implementation of arrays ?
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Question by:peiyoke
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2 Comments
 
LVL 8

Accepted Solution

by:
Answers2000 earned 50 total points
ID: 1252243
Depends on the compiler.

Assuming DOS or Win3.1 (you mention code segment which implies you are compiling small or medium model on one of these)
64*64*2 (array of shorts) = 8192 bytes
64*64*4 (array of floats) = 16384 bytes

A segment in these environments is 64K.

The easiest solution is to change to LARGE model (in your compiler options).  In DOS/Win3.1 any single variable can be up to 64K in these models.

so
512*512*2 (shorts) = 524288 bytes
512*512*4 (floats) = 1048576 bytes.

Unfortunately this still doesn't fit in one segment.

What you have to is
1. Allocate the memory (GlobalAlloc then GLobalLock in Windows, or compiler specific huge-malloc function in DOS)
2. Cast the pointer to the of the array into a huge pointer
3. Calc position in the array, something like
long offset = (long)( column * sizeof(short) ) + (long)( row * 512 * sizeof(short) )
item_address = start_of_memory + offset
(substitue sizeof(float) for the float arrays)).
4. Access memorys in the array by doing
*item_address = value
or
value = *item_address ;
5. When done free the memory (GlobalUnlock then GlobalFree in Windows, or free in DOS)

For DOS you will need also need a DPMI (DOS Protected Mode Interface) capable compiler or a compiler than knows about DOS extenders.

BTW if you have read in an old Petzold (Win 3.1 version) that Large version is bad news, this only applies to MS C versions 5.1 and 6 - it is fixed in MS C 7.0, MS C 8 and all versions of Visual C and Borland C.

If you switch to NT, Win95 or UNIX you will not have these problems and can declare arrays any size.


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LVL 11

Expert Comment

by:alexo
ID: 1252244
For DOS or Windows 3.x try:
    huge float rn[HEIGHT][WIDTH], ...
    ^^^^^
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