Q104644: INFO: Passing C Arrays to MASM by Reference
Article: Q104644
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): kbLangC kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600
Last Modified: 29-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 sample code below demonstrates how to pass C arrays of type char, short, and
long to a Microsoft Macro Assembler (MASM) procedure by reference.
MORE INFORMATION
================
The samples below include one C file and three different assembly files. The
three assembly files demonstrate how to pass variables by reference in small
model 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++ 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
#include <stdio.h>
#ifdef __cplusplus
extern "C" {
#endif
void MasmSub (char *, short *, long *);
#ifdef __cplusplus
}
#endif
char chararray[4] = "abc";
short shortarray[3] = {1, 2, 3};
long longarray[3] = {32768, 32769, 32770};
main ()
{
printf ("%s\n", chararray);
printf ("%d %d %d\n", shortarray[0], shortarray[1], shortarray[2]);
printf ("%ld %ld %ld\n", longarray[0], longarray[1], longarray[2]);
MasmSub (chararray, shortarray, longarray);
printf ("%s\n", chararray);
printf ("%d %d %d\n", shortarray[0], shortarray[1], shortarray[2]);
printf ("%ld %ld %ld", longarray[0], longarray[1], longarray[2]);
}
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
.286
.CODE
MasmSub PROC uses si, \
arraychar:PTR, \
arrayshort:PTR, \
arraylong:PTR
mov si, arraychar ; Load SI with the address of the char array.
mov BYTE PTR [si], "x" ; Since a char is 1 byte long, each
mov BYTE PTR [si+1], "y" ; successive element can be accessed
mov BYTE PTR [si+2], "z" ; by adding 1 more to si.
mov si, arrayshort ; Load SI with the address of the short array.
add WORD PTR [si], 7 ; Since a short is 2 bytes long, each
add WORD PTR [si+2], 7 ; successive element can be accessed
add WORD PTR [si+4], 7 ; by adding 2 more to si.
mov si, arraylong ; Load SI with the address of the long array.
add WORD PTR [si], 1 ; Since a long is 4 bytes long, each
adc WORD PTR [si+2], 0 ; successive element in the array
add WORD PTR [si+4], 1 ; can be accessed by adding 4 more
adc WORD PTR [si+6], 0 ; to si (or 4 more to si+2 to access
add WORD PTR [si+8], 1 ; the high word of each element).
adc WORD PTR [si+10], 0
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
.286
.CODE
MasmSub PROC uses es si, \
arraychar:PTR, \
arrayshort:PTR, \
arraylong:PTR
les si, arraychar ; Load ES:SI with the address of the char array.
mov BYTE PTR es:[si], "x" ; Since a char is 1 byte long, each
mov BYTE PTR es:[si+1], "y" ; successive element can be accessed
mov BYTE PTR es:[si+2], "z" ; by adding 1 more to si.
les si, arrayshort ; Load ES:SI with the address of the short array.
add WORD PTR es:[si], 7 ; Since a short is 2 bytes long, each
add WORD PTR es:[si+2], 7 ; successive element can be accessed
add WORD PTR es:[si+4], 7 ; by adding 2 more to si.
les si, arraylong ; Load ES:SI with the address of the long array.
add WORD PTR es:[si], 1 ; Since a long is 4 bytes long, each
adc WORD PTR es:[si+2], 0 ; successive element in the array
add WORD PTR es:[si+4], 1 ; can be accessed by adding 4 more
adc WORD PTR es:[si+6], 0 ; to si (or 4 more to si+2 to access
add WORD PTR es:[si+8], 1 ; the high word of each element).
adc WORD PTR es:[si+10], 0
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 flat, C
.CODE
MasmSub PROC uses esi, \
arraychar:PTR, \
arrayshort:PTR, \
arraylong:PTR
mov esi, arraychar ; Load ESI with the address of the char array.
mov BYTE PTR [esi], "x" ; Since a char is 1 byte long, each
mov BYTE PTR [esi+1], "y" ; successive element can be accessed
mov BYTE PTR [esi+2], "z" ; by adding 1 more to esi.
mov esi, arrayshort; Load ESI with the address of the short array.
add WORD PTR [esi], 7 ; Since a short is 2 bytes long, each
add WORD PTR [esi+2], 7 ; successive element can be accessed
add WORD PTR [esi+4], 7 ; by adding 2 more to esi.
mov esi, arraylong ; Load ESI with the address of the long array.
inc DWORD PTR [esi] ; Since a long is 4 bytes long, each
inc DWORD PTR [esi+4] ; successive element can be accessed
inc DWORD PTR [esi+8] ; by adding 4 more to esi.
ret
MasmSub ENDP
END
The following is the output of the program:
abc
1 2 3
32768 32769 32770
xyz
8 9 10
32769 32770 32771
Additional query words: mixed language
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Keywords : 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 : kbinfo
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