Assigning Functions to Overlays Using MOVE

The information in this article applies to:

• Microsoft LINK for MS-DOS, versions 5.3, 5.31, 5.5, and 5.6

SUMMARY

The text below is designed to supplement section 15.2, "How to Create an Overlaid Program" in the Microsoft C/C++ "Environment and Tools" manual for version 7.0. Specifically, the article provides additional details about using the FUNCTIONS statement in a module-definition (.DEF) file to create an application that uses the Microsoft Overlaid Virtual Environment (MOVE). It does not discuss using the SEGMENTS statement to assign code segments to overlays. For information on the latter process, query in the Microsoft Knowledge Base on the following words:

   file4.c and overlaid and segments and move and resident and def

Consider an application that contains three source files. The functions in the files are as follows:

   MAIN.C:
           int main(void);

   MOD1.C:
           int __cdecl func11(int);
           int __cdecl func12(int);
           int __cdecl func13(int);

   MOD2.C:
           int __pascal func21(int);
           int __pascal func22(int);

To use the FUNCTIONS statement, packaged functions and the medium or large memory model are required. The following compiler command line satisfies these requirements:

   cl /c /AM /Gy main.c mod1.c mod2.c

The .DEF file specifies the organization of the overlays. An appropriate LINK command line is as follows:

   link main mod1 mod2, test.exe, test.map /MAP,, ovl.def

As the first example, the following .DEF file places func11 and func21 into an overlay. LINK puts the functions into a comdat_seg2 segment in overlay 1 (as indicated in the map file). The other functions remain in the comdat_seg1 segment in the resident portion of the program.

Sample DEF File #1

   NAME test.exe
   FUNCTIONS:1 _func11 FUNC21

As a second example, consider the following .DEF file:

Sample DEF File #2

   NAME test.exe
   FUNCTIONS:1 _func11 FUNC22
   FUNCTIONS:2 _func12