would this work?

[stupid_mutt]

I want to load a really small .com file (like 200 bytes or something) into an array and then run it. Am I doing this right?

int main()
{
unsigned char program[500]; // to store the program
int i; //some crap for some crap
FILE *fp; //to load the program

for(i=0i;<500;i++) // clear the array
program[i]='\0';

fp=fopen("program.com", "rb");

i=0;

while( program[i]=fgetc(fp) !=EOF ); // load it up

// sorry, donno how to do it without asm

asm{
mov bx, program[0]
jmp bx
}

return 0;
}

Do you think this would work or would I have to do it differently.

[quzah]

Um... why?

system("mycomfile.com");

Quzah.

[stupid_mutt]

well... would that work?

[Salem]

No it wouldn't, because

1. You need to load the .com file aligned on a 16 byte boundary

2. you need to save all your registers, and set some others.

3. COM files can exit with a DOS interrupt, which will most likely take your program down with it.

Here's some info
http://www.acc.umu.se/~john/TAE/c001p16.htm

You might be able to make it work for some files, but you're going to get pretty close to doing what system() does anyway.

[stupid_mutt]

The reason Im not using system() is because I want to try to make a simple little multitasking thing (a kernel I guess) that can load a couple of .com files (exe would probably be too hard) and switch betwen them 18.2 (int 1CH I think) times per second. Ok moving on, so I guess the psp is something that dos puts at [segment:0] and the actuall .com file is put at [segment:100H], is this right? If Im correct about that then couldnt I just load a file with no dos exit functions and at the end of the array that I load it into put a jmp instruction to wherever I want it to go once its finished?

[Salem]

As far as I know, a .COM file begins with a PSP, which DOS overwrites with a few bits of information which are applicable at run time.

It still wouldn't work, because DOS itself isn't re-entrant, so if you switched tasks whilst "a.com" was in the middle of a DOS function, and "b.com" tried to use DOS, then you're stuck - dunno what would happen.

[stupid_mutt]

so your saying that like if program 1 called an int 21 function and then it switched to the next program in the middle of that call and that new program also called int 21 then it could get ugly. damn this could be tough, any alternatives you an think of?

[Salem]

Do you have the source for these .COM files?

[stupid_mutt]

nope. I would want my thing to be able to run any .com program so theres no way of knowing what it will run. It wouldnt work even if I saved all the registers before I had it switch to the other program?

[Salem]

> It wouldnt work even if I saved all the registers before I had it switch to the other program?
No.

If you're trying to write a kernel, then look around here
http://www.google.com/search?hl=en&q=ctask+kernel

I think you can get the source for ctask, and it will show you all the grubby bits you need to take care of, to persuade multi-tasking to run on DOS.

Hopefully, it will allow you to see how to adapt your idea.