Access contents of pre-specified memory address

[pole1080]

Hello, I am attempting to write some code to be executed in MS-DOS that will copy data from the 0xC000 segment into the 0x8000 segment (this has to do with the video bios).

My problem is that I can not figure out how to access the contents of a specific memory address. From what I have been reading this can be done is DOS, obviously not in windows though.

I see that 'far pointers' will be needed to accomplish this since the data are in two different segments (the memory is represented as segment: offset), but can't seem to even be able to write code that will read the contents of a specified memory address and display them in a printf statement.

For example, can anyone show me how to access the contents of memory address 0xC0000000 and print the contents out in a printf statement?

Any help is greatly appreciated.

[Salem]

DOS compilers usually had some kind of MKFP macro to make a far pointer for you.

[pole1080]

i found the macro in the dos.h file but i don't know how to use it.

#define _MK_FP(seg, offset) (void __far *)(((unsigned long)seg << 16) \
+ (unsigned long)(unsigned)offset)

[Salem]

Like
void *p = _MK_FP(0xc000,0x0000)

[pole1080]

ok thanks, i figured that part out. now for the second part. how do i change the INT10 vector to point to 8000h segment?

[itCbitC]

ok thanks, i figured that part out. now for the second part. how do i change the INT10 vector to point to 8000h segment?

In <dos.h> there's a union struct called REGS. Create a variable of that type, initialize its member ax to to 0x8000. Now invoke the BIOS services thro' int86() with 0x10 as its first argument.