PRB: C2440 When Initializing an Object Within an Object

• Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5
• Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 4.0, 4.1, 4.2, 5.0, 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
Version : WINDOWS:1.0,1.5;WINDOWS NT:1.0,2.0,4.0,4.1,4.2,5.0
Platform : NT WINDOWS
Issue type : kbprb