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Q34372: Unresolved Externals Link Errors for OS/2 Calls

Article: Q34372
Product(s): See article
Version(s): 5.10   | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 20-OCT-1988

Question:

Why do I get unresolved externals for all of my API calls when I link
object files produced by the C Version 5.10 compiler?

Response:

You can control the OS/2 files to include by defining certain symbols
in your source code. A few of the more common ones are listed below:

#define INCL_BASE        /*  all OS/2 base definitions        */
#define INCL_DOS         /*  OS/2 DOS kernel                  */
#define INCL_SUB         /*  VIO, keyboard, mouse functions   */
#define INCL_DOSERRORS   /*  OS/2 errors                      */

One or more of the above definitions should be followed by the
following:

#include <os2.h>

The above #defines and #include preprocessor directives will start a
chain reaction of #defines and #includes that will define the API
functions in the respective categories of functions. You can follow
this series to determine the minimum prototypes required for the API
functions called by your application.

If the proper constant is not defined in your source code above the
line where you include OS2.H, there will be no prototypes for API
functions.

All of the API functions must be declared with the Pascal calling
convention. If there are no prototypes to tell the compiler to use the
Pascal calling convention, the compiler will use the default C calling
convention. The C calling convention will place an underscore (_) in
front of each function called; therefore, each function will be
incorrectly named, resulting in unresolved externals at link time. The
Pascal calling convention does not place an underscore in front of
each function, so if the correct prototypes are given, the linker will
resolve all of the references to the API functions in the DOSCALLS.LIB
library.

This information is documented in the README.DOC file that comes with
Microsoft C Version 5.10.

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