Microsoft KB Archive/104616: Difference between revisions
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The sample code below demonstrates how to share variables of type char, short, and long between a Microsoft C program and a Microsoft Macro Assembler (MASM) program. This is accomplished by declaring the C variables outside the a function definition, which makes them public. The MASM subprogram can gain access to these public variables by declaring them with the EXTRN directive. The EXTRN directive has the following format | The sample code below demonstrates how to share variables of type char, short, and long between a Microsoft C program and a Microsoft Macro Assembler (MASM) program. This is accomplished by declaring the C variables outside the a function definition, which makes them public. The MASM subprogram can gain access to these public variables by declaring them with the EXTRN directive. The EXTRN directive has the following format | ||
<pre class="fixed_text"> EXTRN | <pre class="fixed_text"> EXTRN <name>:<type> | ||
</pre> | </pre> | ||
where | where <name> represents the public name of the variable as it is declared in the main module, and <type> can be either BYTE, WORD, DWORD, FWORD, QWORD, or TBYTE. Note that in MASM 6.0 and later, EXTRN is a synonym for EXTERN. If you are using MASM 6.x, then you should use EXTERNDEF, because it is more flexible when used in different contexts. | ||
</div> | </div> | ||
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// Compile options needed: /c | // Compile options needed: /c | ||
#include | #include <stdio.h> | ||
#ifdef __cplusplus | #ifdef __cplusplus | ||
Line 92: | Line 92: | ||
main () | main () | ||
{ | { | ||
while (shortvar | while (shortvar < 11) // Display and increment variables 11 times | ||
{ | { | ||
printf ("%c %d %ld\n", charvar, shortvar, longvar) ; | printf ("%c %d %ld\n", charvar, shortvar, longvar) ; |
Revision as of 13:41, 20 July 2020
Article ID: 104616
Article Last Modified on 7/5/2005
APPLIES TO
- Microsoft C Professional Development System 6.0a
- Microsoft C Professional Development System 6.0a
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 1.5 Professional Edition
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 2.0 Professional Edition
- Microsoft Visual C++ 4.0 Standard Edition
- Microsoft Visual C++ 5.0 Standard Edition
- Microsoft Visual C++ 6.0 Service Pack 5
This article was previously published under Q104616
SUMMARY
The sample code below demonstrates how to share variables of type char, short, and long between a Microsoft C program and a Microsoft Macro Assembler (MASM) program. This is accomplished by declaring the C variables outside the a function definition, which makes them public. The MASM subprogram can gain access to these public variables by declaring them with the EXTRN directive. The EXTRN directive has the following format
EXTRN <name>:<type>
where <name> represents the public name of the variable as it is declared in the main module, and <type> can be either BYTE, WORD, DWORD, FWORD, QWORD, or TBYTE. Note that in MASM 6.0 and later, EXTRN is a synonym for EXTERN. If you are using MASM 6.x, then you should use EXTERNDEF, because it is more flexible when used in different contexts.
MORE INFORMATION
The samples below include one C file and two different assembly files. The two assembly files demonstrate how to share variables 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 void MasmFunc(void); char charvar = 'a'; // Declaring variables outside short shortvar = 1; // of a function definition long longvar = 32768L; // makes them public. #ifdef __cplusplus } #endif main () { while (shortvar < 11) // Display and increment variables 11 times { printf ("%c %d %ld\n", charvar, shortvar, longvar) ; MasmFunc () ; } }
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 .DATA ; NOTE: You can put these as EXTERNDEF ; in .INC file and include it here. EXTRN charvar:BYTE ; The EXTRN directive enables a MASM EXTRN shortvar:WORD ; procedure to access public variables. EXTRN longvar:DWORD .CODE MasmFunc PROC inc charvar inc shortvar add WORD PTR longvar, 1 adc WORD PTR longvar+2, 0 ret MasmFunc 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 .DATA ; NOTE: You can put these as EXTERNDEF ; in .INC file and include it here. EXTERNDEF charvar:BYTE ; The EXTRN directive enables a MASM EXTERNDEF shortvar:WORD ; procedure to access public variables. EXTERNDEF longvar:DWORD .CODE MasmFunc PROC inc charvar inc shortvar inc longvar ret MasmFunc ENDP END
The following is the output of the program:
a 1 32768 b 2 32769 c 3 32770 d 4 32771 e 5 32772 f 6 32773 g 7 32774 h 8 32775 i 9 32776 j 10 32777
Additional query words: 8.00 8.00c 9.00 mixed language
Keywords: kbinfo kbcode kbcompiler KB104616