Q103725: HOWTO: Pass Common C Types to MASM by Reference
Article: Q103725
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,2.0,4.0,5.0,6.0,7.0
Operating System(s):
Keyword(s): kbcode kbLangC kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600
Last Modified: 13-NOV-2001
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The information in this article applies to:
- Microsoft C for MS-DOS
- Microsoft C for OS/2
- Microsoft C/C++ for MS-DOS, version 7.0
- Microsoft Visual C++, versions 1.0, 1.5, 2.0, 4.0
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0
- Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0
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SUMMARY
=======
The following sample code demonstrates how to pass variables of type char,
short, and long from a Microsoft C program to a Microsoft Macro Assembler (MASM)
program by reference.
MORE INFORMATION
================
The following sample includes one C file and three different assembly files. The
three assembly files demonstrate how to pass variables by reference in small and
large model for MS-DOS and in flat model for Windows NT. Link only the
appropriate assembly module to the C module.
Note that MASM 6.1 or later and the C/C++ version 8.0 32-bit compiler that ships
with Visual C++, 32-bit Edition, are required to build the flat model Windows NT
version.
Sample Code
-----------
// Filename: CMAIN.C
// Compile options needed: /c (and /AL for large model)
#include <stdio.h>
extern void MasmSub (char *, short *, long *);
char charvar = 'a';
short shortvar = 1;
long longvar = 32768L;
void main (void)
{
printf ("%c %d %ld\n", charvar, shortvar, longvar);
MasmSub (&charvar, &shortvar, &longvar);
printf ("%c %d %ld", charvar, shortvar, longvar);
}
Sample Code for MS-DOS Small Model Version
------------------------------------------
; Filename: MASMSUB.ASM
; Assemble options needed for MASM: /MX
; Assemble options needed for ML: /c /Cx
.MODEL small, C ;.MODEL ... C tells the assembler that
.286 ; parameters are pushed from right to left.
.CODE
MasmSub PROC uses si, \
pchar:PTR, \
pshort:PTR, \
plong:PTR
mov si, pchar ;Load SI with the address of the char variable.
mov BYTE PTR [si], "z"
mov si, pshort ;Load SI with the address of the short variable.
add WORD PTR [si], 9
mov si, plong ;Load SI with the address of the long variable.
add WORD PTR [si], 1 ;Increment the low word of the long variable
;by 1.
adc WORD PTR [si+2],0 ;Increment the high word.
ret
MasmSub ENDP
END
Sample Code for MS-DOS Large Model Version
------------------------------------------
; Filename: MASMSUB.ASM
; Assemble options needed for MASM: /MX
; Assemble options needed for ML: /c /Cx
.MODEL large, C ;.MODEL ... C tells the assembler that
.286 ; parameters are pushed from right to left.
.CODE
MasmSub PROC uses es si, \
pchar:PTR, \
pshort:PTR, \
plong:PTR
les si, pchar ;Load ES:SI with the address of the char variable.
mov BYTE PTR es:[si], "z"
les si, pshort ;Load ES:SI with the address of the short
;variable.
add WORD PTR es:[si], 9
les si, plong ;Load ES:SI with the address of the long variable.
add WORD PTR [si], 1 ;Increment the low word of the long variable
;by 1.
adc WORD PTR [si+2],0 ;Increment the high word.
ret
MasmSub ENDP
END
Sample Code for Windows NT Flat Model Version
---------------------------------------------
; Filename: MASMSUB.ASM
; Assemble options needed for ML: /c /Cx /coff
.386 ;.MODEL ... C tells the assembler that
.MODEL flat, C ; parameters are pushed from right to left.
.CODE
MasmSub PROC uses esi, \
pchar:PTR, \
pshort:PTR, \
plong:PTR
mov esi, pchar ;Load ESI with the address of the char variable.
mov BYTE PTR [esi], "z"
mov esi, pshort ;Load ESI with the address of the short
;variable.
add WORD PTR [esi], 9
mov esi, plong ;Load ESI with the address of the long variable.
inc DWORD PTR [esi] ;Increment the long variable by 1.
ret
MasmSub ENDP
END
The following is the output of the program:
a 1 32768
z 10 32769
Additional query words: 8.00 9.00 mixed language
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Keywords : kbcode kbLangC kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600
Technology : kbVCsearch kbVC400 kbAudDeveloper kbZNotKeyword8 kbvc150 kbvc100 kbCCompSearch kbZNotKeyword3 kbCVC700DOS kbVC500 kbVC600 kbVC200 kbVC32bitSearch kbVC500Search
Version : :1.0,1.5,2.0,4.0,5.0,6.0,7.0
Issue type : kbhowto
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