Q98989: FIX: Constructor C4705 Warning from Aggregate Class Member

Article: Q98989
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,1.51,1.52,2.0,2.1,2.20
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbVCkbbuglist kbfixlist
Last Modified: 26-JUL-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft C/C++ Compiler (CL.EXE), included with:
   - Microsoft C/C++ for MS-DOS, version 7.0 
   - Microsoft Visual C++, versions 1.0, 1.5, 1.51, 1.52 
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, versions 1.0, 2.0, 2.1, 2.20 
-------------------------------------------------------------------------------

SYMPTOMS
========

When Microsoft C/C++ compiles an application, it generates the following message
for each class constructor:

  warning C4705: statement has no effect

CAUSE
=====

The source code has an embedded aggregate member (class, struct, or union) in a
class definition and the compiler command line includes the /W4 and /f- compiler
options. Note that the /f- option is not supported in the Microsoft Visual C++
32-bit compiler.

RESOLUTION
==========

The C4705 warning is incorrect and can be safely ignored. If the embedded
aggregate is a class, define a default constructor. This will supress the
warning.

STATUS
======

Microsoft has confirmed this to be a bug in the products listed at the beginning
of this article. This problem was fixed in Microsoft Visual C++, version 4.0.

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

The C4705 warning usually indicates a statement does not affect program
execution. Each of the following statements causes this particular warning:

     num - 1270;
     count != 15;
     42;

The code example below demonstrates a structure data member that generates the
C4705 warning for each class constructor. The warning also occurs if the example
used a class or a union instead of a structure.

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

  /* Compile options needed: /W4 /f- (Remove /f- for 32-bit compiler)
  */ 

  #include <iostream.h>

  struct MyStruct_tag { int i; };

  class CMyClass {
     private:
        MyStruct_tag MyStruct;
     public:
        inline CMyClass() { MyStruct.i = 0; };
        inline CMyClass(int init) { MyStruct.i = init; };
        void Print(const char *);
  };

  void CMyClass::Print(const char* string)
  {
     cout << string << MyStruct.i << endl;
  }

  void main(void)
  {
     CMyClass Object1;
     CMyClass Object2(1024);

     Object1.Print("Object1.MyStruct.i = ");
     Object2.Print("Object2.MyStruct.i = ");
  }

Additional query words: 7.00 8.00 8.00c 9.00 9.10 1.00 1.50 1.51 2.00 2.10 2.20

======================================================================
Keywords          : kbCompiler kbCPPonly kbVC kbbuglist kbfixlist
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : :1.0,1.5,1.51,1.52,2.0,2.1,2.20
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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