BUG: L2029 When Using struct with "volatile" Keyword

The information in this article applies to:

• The Microsoft C/C++ Compiler (CL.EXE) included with:

      - Microsoft C/C++ for MS-DOS, version 7.0
      - Microsoft Visual C++ for Windows, versions 1.0 and 1.5
  

SYMPTOMS

A communal (that is, global and uninitialized) structure declaration of a variable with the "volatile" type qualifier is not resolved at link time. The result is an unresolved external (L2029 error) on the declared variable. For example, if the following code

   struct a { int x; } volatile v;

   main() {
     v.x=3;
   }

   error L2029: '_v' : unresolved external

RESOLUTION

Use one of the following three workarounds:

• Use the C++ compiler. This error does not occur with the C++ compiler. If the file is changed to TEST.CPP (in the example above) then it will build without generating this error.

  -or-

• Initialize the variable. This error only occurs if a noninitializing communal declaration is used.

        struct a { x; } volatile v = { 3 };
  

  -or-

• Declare the structure with a tag and use the tag later to declare the variable:

        struct a { x; };
        struct a volatile v;
  

STATUS

Microsoft has confirmed this to be a bug in C/C++ versions 7.0 and 8.0 for MS-DOS and C/C++ version 7.0 for OS/2. This problem does not occur with the Microsoft Visual C++ 32-bit edition.