Article ID: 104617
Article Last Modified on 6/1/2005
APPLIES TO
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 1.5 Professional Edition
- Microsoft Visual C++ 2.0 Professional Edition
- Microsoft Visual C++ 4.0 Standard Edition
- Microsoft Visual C++ 5.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 5.0 Professional Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition
This article was previously published under Q104617
SUMMARY
The sample code below demonstrates how to pass a short from a program that is written in Microsoft C to a procedure that is written with the Microsoft Macro Assembler (MASM). The MASM function also returns a short to the C program.
Registers are used to return values of simple data types. For 16-bit code, such as an MS-DOS program, use the following conventions for returning data to a C program:
char AL
short, int, near * AX
long, far * DX: High order portion (segment)
AX: Low order portion (offset)
For 32-bit code, such as a Windows NT program, use the following conventions for returning data to a C program:
char AL
short AX
long, int, * EAX
The samples below include one C file and two different assembly files. The two assembly files demonstrate how to pass a variable in small 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
short MasmSub(short);
#ifdef __cplusplus
}
#endif
main ()
{
short var = 1;
printf ("%d\n", var);
printf ("%d", MasmSub(var));
}
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, \
sVar:WORD
mov ax, sVar ; Load the short into AX.
add ax, 32766 ; Because the function returns a short (a 2-byte
ret ; value), C will get the return value from AX.
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, \
sVar:WORD
mov ax, sVar ; Load the short into AX.
add ax, 32766 ; Because the function returns a short (a 2-byte
ret ; value), C will get the return value from AX.
MasmSub ENDP
END
The following is the output of the program:
1
32767
Additional query words: mixed language
Keywords: kbhowtomaster kblangc kbcode KB104617
