Q121888: PRB: C2440 When Initializing an Object Within an Object

Article: Q121888
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,2.0,4.0,4.1,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbVC kbVC100 kbVC150 kbVC200 kbVC400 kbVC410 kbVC420 kbVC500 kbVC6
Last Modified: 11-FEB-2002

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

- Microsoft Visual C++, versions 1.0, 1.5, 2.0, 4.0, 4.1 
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

If an object is used to initialize an embedded structure, the compiler produces
error C2440: 'initializing': cannot convert from '<type1> ' to
'<type2> '.

CAUSE
=====

This behavior is by design. Although an aggregate that is a class may be
initialized with an object of its class, there is not a similar provision for
subaggregates.

RESOLUTION
==========

To work around this behavior, use a member by member initialization.

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

The following sample code demonstrates this problem and its resolution. The
error produced in the initialization of two2 is error C2440: 'initializing' :
cannot convert from 'struct ::One ' to 'int '.

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

  /* Compile options needed: none
  */ 

  struct One
  {
     int  i;
  };

  struct Two
  {
     int  j;
     One  one;
     int  k;
  };

  One one1 = { 3 };              // Initialize structure member - OK

  One one2 = one1;               // Initialize structure - OK

  Two two1 = { 1, one1, 3 };     // Error, can not initialize subaggregate

  Two two2 = { 1, one1.i, 3 };   // Member by member initialization - OK

Additional query words: 8.00 8.00c 9.00 10.00 11.00

======================================================================
Keywords          : kbCompiler kbCPPonly kbVC kbVC100 kbVC150 kbVC200 kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbvc150 kbvc100 kbVC410 kbVC420 kbVC500 kbVC600 kbVC200 kbVC32bitSearch kbVC500Search
Version           : :1.0,1.5,2.0,4.0,4.1,4.2,5.0,6.0
Issue type        : kbprb

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

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.