How to make a .com file using C/C++?

Question

How can we make a .com file using C/C++? Is it possible?

Edit: I was able to successfully make a com file using darin's suggestions. But somehow the exe file of the following program cannot be converted to com file. I get the "File cannot be converted" message by exe2bin. I'm using Borland Turbo C++ 3.0. Any suggestions?

#include <dos.h>
void interrupt (*oldint65)( );
char st[80] = {"Hello World$"};
void interrupt newint65(void);
void main()
{
    oldint65 = getvect(0x65); 
    setvect(0x65, newint65);
    geninterrupt (0x65);
    geninterrupt (0x65);
    geninterrupt (0x65);
    setvect(0x65, oldint65);
}
void interrupt newint65( )
{
     _AH = 0x09;
     _DX=(unsigned int)st;
     geninterrupt (0x21);
}

Cause: The program to be converted has one of the following problems: * The program has an origin of 0100h but a different entry point. * The program requires segment fixups. * The program code and data are larger than 64 KB. * The program has more than one declared segment * The file is not a valid .EXE-format file. — Kenneth Cochran
– Kenneth Cochran, Commented Apr 20, 2009 at 19:04

Darin Dimitrov · Accepted Answer · 2009-04-18 15:38:35Z

17

In C, you must compile your program with the TINY memory model. Then you can use use EXE2BIN or a similar program to convert an EXE file to a COM file.

answered Apr 18, 2009 at 15:38

Darin Dimitrov

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Lucas Jones · Accepted Answer · 2009-04-18 15:35:42Z

3

That would depend on what you mean. Do you want to compile your program into a .com file? That would depend on your compiler, if it is possible at all.
If you are writing a compiler (or something like that), and want to produce a .com file from your own program, you should have a look at the COM article on Wikipedia, or use the NASM assembler to assemble to a .com file: nasm -o hello.com hello.asm.

answered Apr 18, 2009 at 15:35

Lucas Jones

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Comments

none · Accepted Answer · 2009-05-20 22:21:03Z

1

Also, it's probably worth pointing out that you seem to be doing TSR programming, which is unlikely to work fully or even properly on non-DOS (i.e. modern) operating systems such as Windows XP/Vista.

You might want to consider running a DOS emulator such as bochs, which also makes it easier to run legacy development tools such as TC++

answered May 20, 2009 at 22:21

none

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