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Pointer to 2D array in function call

 
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pet007



Joined: 25 Jan 2023
Posts: 21

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Pointer to 2D array in function call
PostPosted: Wed Jan 25, 2023 12:34 pm     Reply with quote

Hello, pls, how to use pointer to 2D array stored in ROM in function call ?
When I used Font array in function as static 2D array, it works well and fast, but I'd like to use various 2D arrays in function call. Thanks a lot.
MCU: 18K26K22

Edit: so this one works, but I have to insert size of 2D array in function call:

Code:

rom u8 Ravie16x16[16][33] = { 
        0x07, 0x00, 0x00, 0x......
        0x0D, 0x01.............

void Nokia_BigUni(rom u8 *FONT[16][33],u8 px,u8 py, int8 c) {
   u8 char_pos,i;
   u8 CharLen;   
   
   if(c < 46) c=46;
   if(c > 57) c=57;
   
   char_pos=(c-46);
   CharLen = *FONT[char_pos][0];


Ttelmah



Joined: 11 Mar 2010
Posts: 19513

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PostPosted: Thu Jan 26, 2023 1:52 am     Reply with quote

That is standard and correct.
In C, an array passed to a function, does not 'know' anything about it's
dimensions. It 'decays' to just a pointer. You have a series of choices:
1) Pass as a single dimensional array of pointers. Each pointer then
points to the second list of elements.
2) Pass as a fixed size array known at compile time (this is what you
are now doing). Technically it is only the last dimension that needs to
be known.
3) Pass as a single dimensional array, and pass the size of the elements
as another variable. Then handle the addressing yourself.

Get a standard C textbook. It'll explain this.
pet007



Joined: 25 Jan 2023
Posts: 21

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PostPosted: Thu Jan 26, 2023 1:55 am     Reply with quote

Thanks, yes, now it's clear for me.
pet007



Joined: 25 Jan 2023
Posts: 21

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PostPosted: Thu Jan 26, 2023 1:53 pm     Reply with quote

So this code below works, as Ttelmah said:
('cols' is length of each "row" in 2D array, listed in 1st post.)

Code:

void Nokia_BigCh(rom u8 *FONT, u8 Cols, u8 px,u8 py, int8 c) {
   u8 i;             
   u16 char_pos;
   u8 CharLen;   
   
   if(c < 46) c=46;
   if(c > 57) c=57;
   
     char_pos=(u16)(c-46)*(u16)Cols;   
      CharLen = FONT[char_pos][0];     
    Nokia_cmd(0x22);
    Nokia_gotoXY(px,py);
   
   CharLen = CharLen << 1; 
   for(i=1;i < CharLen;i=i+2) { 
       Nokia_write(FONT[char_pos][i]);  Nokia_write(FONT[char_pos][i+1]);
....


For simpler call I am using this definition also:
Code:


#define Nokia_RevieNum(x,y,c)  Nokia_BigCh(Ravie16x16,33,x,y,c+46)


so in main.c :

Code:

    Nokia_RevieNum(pos_x, pos_y, digit);   // digit: 0-8

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