Q88092: BUG: Cannot Access Static Data Members in Inline Assembly

Article: Q88092
Product(s): Microsoft C Compiler
Version(s): winnt:1.0,2.0,2.1,4.0,4.1,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbVC100bug kbVC150bug kbVC200bug kbVC210bug kbVC400bug kbVC410bug kbVC500bug kbVC600bug
Last Modified: 03-MAY-2001

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The information in this article applies to:

- The C/C++ Compiler (CL.EXE), used with:
   - Microsoft C/C++ for MS-DOS, version 7.0 
   - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5 
   - Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 4.1, 4.2, 5.0, 6.0 
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SYMPTOMS
========

When trying to access static data members in a C++ program with inline assembly,
the compiler may report the following errors:

  error C2420: 'identifier' : illegal symbol in first operand 1

  error C2415: improper operand type

The inline assembler cannot access static data members within a class member
function. The sample code below demonstrates the problem.

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft products that are
listed at the beginning of this article.

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

To access the static data member, assign the address of the data member to a
temporary variable. The inline assembler can then access the data by loading the
address from the temporary variable.

Below is code that demonstrates the problem and workaround.

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

     /* Compile options needed: /AS  for 16-bit
     *                          none for 32-bit
     */ 

     #include <stdio.h>

     class sample
     {
     public:

        static int value;
        sample();

     };

     int sample::value = 9;

     sample::sample()
     {

          __asm mov value,3             // C2420 and C2415 here
          __asm mov sample::value,ax    // C2420, C2414, C2400 on
                                        // this line

     //  For 16-bit workaround, uncomment next three lines.
     //     void * valueptr=&value;
     //     __asm mov bx, valueptr
     //     __asm mov [bx],3

     //  For 32-bit workaround, uncomment next three lines.
     //     void * valueptr=&value;
     //     __asm mov ebx, valueptr
     //     __asm mov [ebx],3
     }

     int main( void )
     {
        sample aSample;
        printf( "aSample.value = %d.\n", aSample.value );
        return 0;
     }

Additional query words: 8.00 8.00c 9.00 10.00 10.10 10.20

======================================================================
Keywords          : kbVC100bug kbVC150bug kbVC200bug kbVC210bug kbVC400bug kbVC410bug kbVC500bug kbVC600bug 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : winnt:1.0,2.0,2.1,4.0,4.1,4.2,5.0,6.0
Issue type        : kbbug

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