[MSX-C] Q&A official thread

And by the way, I've recovered my old account. :-)

I haven't decided yet whether I'll keep posting as JaviLM or as ag0ny, because this nickname has some history, but I haven't used it for some years. Expect to see messages from both accounts for a few days until I decide which one I'll keep.

Here goes again.

Question: I'm not sure how constant pointers works. I'd like to define a pointer in FBE5H. It's NEWKEY data area, where it's stored if a file of keyboard matrix is read. For example if I want to read key M, I must read row 4 column 2 (this is, second bit in row 4). In order to make that I do the following:

readkey(row,col)
TINY row,col; 
{
    TINY key;
    TINY *adr=0xFBE5;
    key=adr[row] & ((TINY)1<<col);
}

This code works, when M is pressed key value is 0. I'd like to define address as constant so:

#define NEWKEY (*(TINY *)0xFBE5
readkey(row,col)
TINY row,col; 
{
    TINY key;
    key=NEWKEY+row & ((TINY)1<<col);
}

This code doesn't works, it doesn't detect key M pressed, key allways values 0. As you can see I can't use NEWKEY[row], it produces compilation error, so I use alternative way to access *arrays (x+y instead x[y]). I'm clearly reading wrong address. Any idea?

Thanks!

Sorry it was a typo, it's efectively #define NEWKEY (*(TINY *)0xFBE5). You are right, defines are replaced for its value in the compiled code, so perhaps it's something wrong.

I already used option *(NEWKEY+row) but I obtain a compilation error (bad indirection). The other notation (const TINY * NEWKEY = 0xFBE5) doesn't works on MSX-C, it doesn't compile. I think that const it's not supported in MSX-C, if you try a simple "const int life=3;" it gives the same error compilation.

I tryed to follow a code example that makes the following:

#define T32NAM *((int *)0xf3bd)
...
vpoke(T32NAM + (Hy+1) * 32 + (Hx+1), ' ');

As you can see, it uses T32NAM+value to get the address

None, you can use both of them to detect key pressed. Perhaps the advantage of NEWKEY is that you can also use OLDKEY in order to disable functions as autofire.

However I've found the solution

#define NEWKEY (TINY *)0xFBE5

readkb(row,col) 
TINY row,col;
{
    TINY key;
    key=*(NEWKEY+row) & (1<<col);
}

At least it works, thanks for your help . The same code works using snsmat(row).

Yeah, let's paste the final version:

#define NEWKEY (TINY *)0xFBE5

TINY readkb(row,col) 
TINY row,col;
{
    TINY key;
    key=*(NEWKEY+row) & (1<<col);
    return key;
}

With this function on your main loop, you read keyboard .