Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uwm.edu!zaphod.mps.ohio-state.edu!mips!pacbell.com!pacbell!att!cbnewsc!tjr
From: tjr@cbnewsc.att.com (thomas.j.roberts)
Newsgroups: comp.sys.ibm.pc.programmer
Subject: Re: Using Turbo C with libraries compiled with Microsoft C
Message-ID: <1990Jun4.205834.13661@cbnewsc.att.com>
Date: 4 Jun 90 20:58:34 GMT
References: <10760@medusa.cs.purdue.edu>
Organization: AT&T Bell Laboratories
Lines: 43

There are several (many ?) differences between Turbo C and Microsoft C.
Some of them are harmless, some will kill your program; some will kill
MS-DOS, some might even trash your disk(s).

THIS IS PROBABLY NOT A COMPLETE LIST!

1)	TC returns 4-byte results in AX/DX; MC uses AX/BX (float/double
	are returned in 8087 Top-Of-Stack register). This will make any
	large-pointer function misbehave dangerously, and will give
	erroneous results from any long function.
2)	TC and MC use different names for the various segments.
	This will probably prevent it from linking properly (except for
	huge model programs), and will cause subtle errors in a
	huge-model program.
3)	TC and MC package library routines differently, so you cannot
	use both the MC and the TC run-time libraries. If the third-party
	library depends upon the MC run-time library, this may cause
	link and/or run-time problems.
4)	TC and MC have different requirements for subroutines to preserve
	register contents. This will cause a serious disaster during
	execution (write-protect those disks before executing!).
5)	The TC run-time library screws around with the console hardware
	(even if you don't call any of its TEXT or GRAPHICS routines);
	this can often be minimized by setting directvideo=0.

In most cases, even if you manage to get the linker to link the program
and libraries without error, it will still die a horrible death when
executed (usually taking MS-DOS down, too).

In short, I strongly advise against trying to mix compilers in the same
program. If you simply cannot afford to buy the other compiler, then
you probably can make it work with the following kludges:

	1)	use TC huge model, and MC large model.
	2)	wrap every MC library routine with a special assembly
		routine to satisfy BOTH TC and MC register conventions
		(MC routine calling MC routine is probably OK as is).
		This special routine will need to manage DS.

Good luck [you will really need it!].

Tom Roberts
att!ihlpl!tjrob