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Alan Brown
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 Posted: Thu Feb 24, 2005 7:32 am Post subject: Setting Pointer to Video memory |
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Subject: Setting Pointer to Video memory
Newsgroups: Optus:comp.lang.c++.moderated
Hi People,
[Sorry for the cross-posting - my post seems not to have reached the other
group.]
I am trying to create a Help Screen in a program. I want to swap out the
video memory, use the screen, then swap back the original contents of the
screen.
The following is the relevant parts of a program that works -
---------------------------------------------------------
#include <dos.h>;
#include <conio.h>;
...
...
...
struct Scrn // struct for Screen memory
{
char n[4000];
};
...
...
...
void ScreenSwap() // Test swapping windows
{
ShowHeader("Screen Swapping");
int i;
Scrn dest;
for (i=0; i<4000; i++) // Write out Video memory to structure
{
dest.n[i] = peekb(0xb800, 0000 + i);
}
getch(); // Pause...
textcolor(LIGHTRED); // Clear Screen to different colors
textbackground(BLACK);
clrscr();
getch(); // Pause...
for (i=0; i<4000; i++) // Read back from structure into Video memory
{
pokeb(0xb800, 0000 + i, dest.n[i]);
}
getch();
}
...
...
...
---------------------------------------------------------
The above works. But I want to use 'memcopy' or 'memmove' instead. But I
am not able to set a pointer to an absolute address such as 0xB8000000.
If it is possible to do this I would be grateful if someone could help me
please.
Alan
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Raymond Martineau
Guest
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| Posted: Thu Feb 24, 2005 11:06 pm Post subject: Re: Setting Pointer to Video memory |
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On 24 Feb 2005 07:32:22 GMT, Alan Brown <rigelau (AT) yahoo (DOT) nospam.com.au>
wrote:
| Quote: | Subject: Setting Pointer to Video memory
Newsgroups: Optus:comp.lang.c++.moderated
Hi People,
[Sorry for the cross-posting - my post seems not to have reached the other
group.]
I am trying to create a Help Screen in a program. I want to swap out the
video memory, use the screen, then swap back the original contents of the
screen.
|
[...]
| Quote: | The above works. But I want to use 'memcopy' or 'memmove' instead. But I
am not able to set a pointer to an absolute address such as 0xB8000000.
|
The procedure for initializing an absolute address into a pointer (aside
from NULL) is system specific. For example, you might be able to use a
C-style or reinterpret_cast to convert an integer into a void pointer, but
other systems will not allow the user to directly access that memoey.
If a direct cast does not work, you will need to read the documentation
that came with your compiler (or at least try to find out how the your
compiler represents a pointer.)
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Alan Brown
Guest
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| Posted: Fri Feb 25, 2005 2:48 am Post subject: Re: Setting Pointer to Video memory |
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[email]bk039 (AT) ncf (DOT) ca[/email] (Raymond Martineau) wrote in
news:ucns11hrt1dmgd2m54qr9bniif2m53klla (AT) 4ax (DOT) com:
| Quote: |
[Sorry for the cross-posting - my post seems not to have reached the
other group.]
I am trying to create a Help Screen in a program. I want to swap out
the video memory, use the screen, then swap back the original contents
of the screen.
[...]
The above works. But I want to use 'memcopy' or 'memmove' instead.
But I am not able to set a pointer to an absolute address such as
0xB8000000.
The procedure for initializing an absolute address into a pointer
(aside from NULL) is system specific. For example, you might be able
to use a C-style or reinterpret_cast to convert an integer into a void
pointer, but other systems will not allow the user to directly access
that memoey.
If a direct cast does not work, you will need to read the
documentation that came with your compiler (or at least try to find
out how the your compiler represents a pointer.)
|
Thanks for your reply.
I forgot to say that I am using Borland C++ 3.1 under Windows 98SE.
I will try what you suggest. I have no documentation for the compiler
other than the on-line help and some general reference manuals on C and C++
Since my code works OK there is not really a problem - I was looking for a
"neater" way of accessing Video memory.
Thanks again
Alan
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