Question

I have three array, like this, that contains my bitmap images:

static unsigned char __attribute__ ((progmem)) impostazioni_logo[]={

0x00, 0x02, 0x7E, 0x02, 0x00, 0x00, 0x78, 0x10, 0x08, 0x08, 0x08, 0x70, 0x10, 0x08,    0x08, 0x08,
0x70, 0x00, 0x00, 0x78, 0x10, 0x08, 0x08, 0x08, 0x10, 0x60, 0x00, 0x00, 0x60, 0x10, 0x08, 0x08,
0x08, 0x10, 0x60, 0x00, 0x00, 0x30, 0x48, 0x48, 0x08, 0x08, 0x10, 0x00, 0x00, 0x08, 0x7E, 0x08,
0x08, 0x08, 0x00, 0x00, 0x50, 0x48, 0x48, 0x48, 0x70, 0x00, 0x00, 0x08, 0x08, 0x08, 0x48, 0x28,
0x18, 0x00, 0x00, 0x7A, 0x00, 0x00, 0x60, 0x10, 0x08, 0x08, 0x08, 0x10, 0x60, 0x00, 0x00, 0x78,
0x10, 0x08, 0x08, 0x08, 0x08, 0x70, 0x00, 0x00, 0x7A, 0x00, 0x00, 0x08, 0x0F, 0x08, 0x00, 0x00,
0x0F, 0x00, 0x00, 0x00, 0x00, 0x0F, 0x00, 0x00, 0x00, 0x00, 0x0F, 0x00, 0x00, 0x7F, 0x08, 0x08,
0x08, 0x08, 0x04, 0x03, 0x00, 0x00, 0x03, 0x04, 0x08, 0x08, 0x08, 0x04, 0x03, 0x00, 0x00, 0x04,
0x08, 0x08, 0x09, 0x09, 0x06, 0x00, 0x00, 0x00, 0x07, 0x08, 0x08, 0x08, 0x00, 0x07, 0x08, 0x08,
0x08, 0x04, 0x0F, 0x00, 0x00, 0x0C, 0x0A, 0x09, 0x08, 0x08, 0x08, 0x00, 0x00, 0x0F, 0x00, 0x00,
0x03, 0x04, 0x08, 0x08, 0x08, 0x04, 0x03, 0x00, 0x00, 0x0F, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0F,
0x00, 0x00, 0x0F, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  };

Now i want a function return the correct array to display on lcd by passing the page parameter.

unsigned char logo(int page){
 char buffer[32];
  switch(page){
    case 1:
       for(int i=0;i<sizeof(impostazioni_logo);i++){
        strcpy_P(buffer,pgm_read_byte(&(impostazioni_logo[i]))); //<==pgm_read_byte comes from here:http://www.arduino.cc/en/Reference/PROGMEM
       }  
    break;
  }
   return buffer;

}
it doesn’t work. Compiler tell me something wrong about conversion.

EDIT:

caller is a simply function that draw the right image. Images can be different for different pages. Number of pages are near 20:

void drawLogo(){
 glcd.drawbitmap(15,1, logo(), 90,16); //display lcd library for ST7565

}

Answer 1

There are a few issues with this code:

1. return type for logo is unsigned char while you are returning char *
2. pgm_read_byte supposedly returns a byte, so you could simply do buffer[i]=pgm_read_byte(...)
3. buffer that you are trying to return is allocated on the stack and will not exist after function returns.

You should probably be using strlcpy_P instead.

Update:
1. Assuming you have a fixed number of pages. Try creating a bitmap per page, like:

static unsigned char __attribute__ ((progmem)) impostazioni_logo_page1[]={..}

2. return a pointer to each pages’ logo:

unsigned char* logo(int page)
{
  switch(page)
  {
    case 1:
       return impostazioni_logo_page1;
    break;
  }
  return NULL;
}

If you like to have all bitmaps in a single array, calculate an offset in the array and return that instead:

int offset = page_num*page_size_in_chars;    
return &impostazioni_logo_all_pages[offset];

Update 2: Another option to manage pages:

static unsigned char* pages[] = { impostazioni_logo_page1, impostazioni_logo_page2, ... }
...
glcd.drawbitmap(15,1, pages[page_index], 90,16);