FIX: Constructor C4705 Warning from Aggregate Class Member

MS-DOS | WINDOWS             | WINDOWS NT

The information in this article applies to:

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

      - Microsoft C/C++ for MS-DOS, versions 7.0
      - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51 and
        1.52
      - Microsoft Visual C++, 32-bit Edition, versions 1.0, 2.0, 2.1,
        and 2.2
  

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;

Sample Code

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

#include <iostream.h>

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 = ");