## BUG: Bad Code Generated for Based Structures

Q116441

    7.00   | 1.00 1.50
    MS-DOS | WINDOWS
    kbtool kbbuglist

    ----------------------------------------------------------------------
    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 structure or an array of structures that are based in the code segment
    using based pointers may not appear to have the proper values when
    referenced. This happens with both versions 8.0 and 8.0c of the C/C++
    Compiler. With version 7.0 of the C/C++ Compiler, the referenced structure
    values and generated code are correct but the compiler issues a C4762
    warning:

       near/far mismatch in argument; conversion supplied

    CAUSE
    =====

    An instruction needed to load the segment of the array into the ES register
    is not generated. Therefore, the wrong code segment is used for the array.

    RESOLUTION
    ==========

    With the 7.0 version of the compiler, the warning can be safely ignored.
    The warning is not generated if the /f- compiler option is used.

    With the 8.0 and 8.0c versions of the compiler, the __far keyword
    must be used when referencing the array to work around the problem. The
    sample code in the "MORE INFORMATION" section, below, demonstrates the
    problem and the workaround.

    STATUS
    ======

    Microsoft has confirmed this to be a bug in the C/C++ Compiler for
    MS-DOS, versions 7.0, 8.0, and 8.0c. We are researching this problem and
    will post new information here in the Microsoft Knowledge Base as it
    becomes available.

    This is not an issue with the 32-bit compiler.

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

    The following sample code can be used to demonstrate this problem:

    Sample Code
    ===========

    /* Compile options:
          7.0:      use /f- to supress the warning
          8.0/8.0c: use /DFIXED to generate correct code
    */

    #include <stdio.h>

    typedef struct {
       unsigned c:       8;
       unsigned accept:  1;
       unsigned endstat: 1;
       unsigned spare:   6;
       int next;
    #ifdef FIXED
    } __based(__segname("LR_TEXT")) __far VSTAT;
    #else
    } __based(__segname("LR_TEXT")) VSTAT;
    #endif

    #ifdef FIXED
    int findvoc (char c, VSTAT __far a[]);
    #else
    int findvoc (char, VSTAT[]);
    #endif

    void main()
    {
    #ifdef FIXED
       static VSTAT __far va[] = {
    #else
       static VSTAT va[] = {
    #endif
          {'A',  0, 0, 0,   96},
          {'B',  0, 0, 0,  133},
          {'C',  0, 0, 0,  143},
          {'\0', 0, 1, 0,    0}
       };
       int i;

    #ifdef FIXED
       i = findvoc ('C', (VSTAT __far *)va);
    #else
       i = findvoc ('C', va);
    #endif

       printf( "i = %d\n",i );
       return;
    }

    #ifdef FIXED
    int findvoc (char c, VSTAT __far a[])
    #else
    int findvoc (char c, VSTAT a[])
    #endif
    {
       return ((int)a[c - 'A'].c);
    }

    Additional reference words: 1.00 1.50 7.00 8.00 8.00c
    KBCategory: kbtool kbbuglist
    KBSubcategory: CodeGen

Keywords : kb16bitonly
Issue type : kbbug
Technology : kbVCsearch kbAudDeveloper kbCVCComp

Last Reviewed: May 5, 2001 © 2001 Microsoft Corporation. All rights reserved. Terms of Use.