ID Number: Q43052
1.x 2.03 2.10 3.00 3.10
WINDOWS
Summary:
Windows does not support applications coded with OS/2 Family API
(FAPI) calls.
More Information:
FAPI works in the following manner:
1. The code contains references to OS/2 FAPI calls (such as DosOpen,
DosRead, and so on).
2. When the program is loaded into OS/2 protected mode, the system
loader dynamically links the FAPI calls to the OS/2 system-services
DLLs (Dynamic-Link Libraries).
3. When the program is loaded into real mode (MS-DOS or OS/2
compatibility box), what actually gets loaded is a small program
called the "FAPI Loader and Linker." It is this program that loads
the real code; it dynamically links the FAPI calls to a special
library of support routines that translate FAPI calls into 80x86
code and MS-DOS interrupts (INT 21H Function xx).
This process is also described on Page 251 of Gordon Letwin's book
titled "Inside OS/2" (Microsoft Press, 1988).
FAPI works well for programs that need to run in MS-DOS and OS/2
protected mode. The problem is that Windows uses the "New EXE Format"
for programs, bypassing the standard MS-DOS entry point. For example,
if a Windows program is run outside of Windows (in MS-DOS), the
following message appears, and the program terminates:
This program requires Microsoft Windows
MS-DOS is not responsible for this message; the Windows program itself
is responsible. The way the Windows program works is very similar to
OS/2: it uses dual entry points into the .EXE file. In MS-DOS, a short
program that prints the above message runs; however, in Windows, a
true Windows application runs using the other entry point in the .EXE
file.
Therefore, the problem is narrowed down to the following: if the FAPI
Loader and Linker program is run using the standard MS-DOS .EXE file
entry point, and Windows starts an application using a different entry
point, the dynamic linking of the FAPI routines will not occur.
Therefore, FAPI calls cannot be used in Windows applications.
To avoid this problem, do the following:
Instead of using low-level DOS calls (INT 21H Function xx) in a
Windows application and OS/2 API calls (DosRead, DosOpen, and so
on) in a Presentation Manager (PM) application, use the C run-time I/O
routines for all of these applications.
This will work because the Microsoft C Compiler and the run-time
libraries supply versions of the libraries that work in both OS/2 and
MS-DOS. By moving C code to PM and to Windows, it will not be
necessary to rewrite it, and the appropriate conversion routines will
be supplied at link time.
Be sure not to use high-level (stream) I/O routines in C with Windows;
just use the low-level (handles) versions. This topic is discussed in
Charles Petzold's book titled "Programming Windows" (Microsoft Press,
1988), and in other articles in the Microsoft Knowledge Base. For more
information, query on the following words:
prod(winsdk) and c and low and level
Additional reference words: SR# G890110-9309 2.x 2.03 2.1 3.00 3.10 3.x