DOCUMENT:Q86816  15-FEB-2002  [masm]
TITLE   :Mixed C and MASM with MASM Main Language, C Run-Time
PRODUCT :Microsoft Macro Assembler
PROD/VER::5.0,5.1,5.1a,6.0,6.0a,6.0b
OPER/SYS:
KEYWORDS:

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Macro Assembler (MASM), versions 5.0, 5.1, 5.1a, 6.0, 6.0a, 6.0b 
-------------------------------------------------------------------------------

SUMMARY
=======

The following steps should be considered when doing mixed-language programming
between the Microsoft Macro Assembler (MASM) and Microsoft C with MASM as the
main language, but the C startup code is to be brought in to enable the assembly
module to call a C run-time routine:

1. Include the statement

   .MODEL <model>, c

   in the assembly module to ensure that C naming and calling conventions are
   used and that the modules use the same default segments. The <model>
   will be small, medium, compact, or large.

2. Use the END directive in the assembly module, but do not specify the entry
   point.

3. The start of the assembly module should be labeled

   main:

   -or-

   main PROC

   and the label should be made public with the following statement:

   PUBLIC main


4. Include the following statement to force a load of the C startup code:

   EXTRN _acrtused:abs

5. Assemble the assembly module with /Mx to preserve the case of nonlocal names.
   If using MASM version 6.0 or later, use /Cx to preserve the case of nonlocal
   names.

Note that the stack declaration comes from the C startup code. The entry point is
in the C startup code, so no entry point should be specified in the assembler
module with the END directive. Doing so will cause only a part of the necessary
initialization to be performed (that is, a stack will be created, but SS will
not get its segment value).

MORE INFORMATION
================

The following is a mixed-language example. There is one C module and one
assembly module that must be compiled and then linked together. No special link
options are needed.

The example declares two words, arg1 and arg2, calls the C run-time routine
printf to print out their values to the screen, and passes their addresses to a
C routine. The C routine swaps the values of arg1 and arg2. The values of arg1
and arg2 are printed out a second time to show that they have been swapped.

Sample Code
-----------

   /* Compile options needed: none
   */ 

   void ptrswap( int *ptr1, int *ptr2 )
   {
       int temp;

       temp = *ptr1;
       *ptr1 = *ptr2;
       *ptr2 = temp;
   }

   ----------------------------------------------------------------------

   ; Assemble options needed: /Mx

           .MODEL small, c

           .DATA

   arg1    DW     1234
   arg2    DW     4321
   format1 DB     "Arg1: %d", 10, 0      ; Format string for printf
   format2 DB     "Arg2: %d", 10, 10, 0  ; Format string for printf

   EXTRN  _acrtused:abs              ; Bring in C startup

           .CODE

   EXTRN  ptrswap:proc               ; External C routine
   EXTRN  printf:proc                ; External C run-time routine
   PUBLIC main                       ; C startup requires the name _main

   main:
           MOV    ax, arg1
           PUSH   ax                 ; Push 2nd argument (C convention)
           MOV    bx, offset format1
           PUSH   bx                 ; Push 1st argument (C convention)
           CALL   printf             ; Call C run-time routine

           MOV    ax, arg2
           PUSH   ax                 ; Push 2nd argument (C convention)
           MOV    bx, offset format2
           PUSH   bx                 ; Push 1st argument (C convention)
           CALL   printf             ; Call C run-time routine

           MOV    bx, offset arg2
           PUSH   bx                 ; Push 2nd argument (C convention)
           MOV    bx, offset arg1
           PUSH   bx                 ; Push 1st argument (C convention)
           CALL   ptrswap            ; Call C routine from module

           MOV    ax, arg1
           PUSH   ax                 ; Push 2nd argument (C convention)
           MOV    bx, offset format1
           PUSH   bx                 ; Push 1st argument (C convention)
           CALL   printf             ; Call C run-time routine

           MOV    ax, arg2
           PUSH   ax                 ; Push 2nd argument (C convention)
           MOV    bx, offset format2
           PUSH   bx                 ; Push 1st argument (C convention)
           CALL   printf             ; Call C run-time routine

           MOV    ah, 4ch            ; Terminate program
           int    21h

           END                       ; Entry point will be specified by
                                     ;    the C startup code

Additional query words: kbinf non-local 5.00 5.10 5.10a 6.00 6.00a 6.00b s_quickasm s_c s_quickc s_qcwin

======================================================================
Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM510 kbMASM600 kbMASM500 kbMASM600a kbMASM510a kbMASM600b
Version           : :5.0,5.1,5.1a,6.0,6.0a,6.0b

=============================================================================

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