Re: [Sdcc-user] pic16f877a function call destroys pointer

[Raphael N. <rn...@we...>]

Hi,

> Program displays just T[glyph/rand char][glyph/rand char][glyph/rand  
> char] [glyph/rand char].
>
> Why is this happening and how can I prevent it? Thanks.

You perform pointer arithmetics on generic pointers (*(s+1)), and thus
triggered a compiler bug which assigned only the lower 2 byte (of the
3 byte generic pointer) to the (temporary) result. The subsequent
dereference of course evaluated all three bytes of the pointer -- but
as the MSB was uninitialized, we accessed random memory locations,
causing your program to display [glyph/rand char] for s+1, s+2, and s+3.

You can prevent it by (a) updating to sdcc 2.9.4, >= r5568 (either using
a snapshot or the svn head) or (b) by avoiding generic pointers,
replacing them with __data pointers:

unsigned char text[10];

void LCD_String(__data unsigned char *s)
{
   LCD_Char(*s);
   LCD_Char(*(s+1));
   LCD_Char(*(s+2));
   LCD_Char(*(s+3));
}

Thank you for reporting this bug.

Raphael