Microsoft KB Archive/121888

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

Article ID: 121888

Article Last Modified on 12/1/2003

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APPLIES TO


 * Microsoft Visual C++ 1.0 Professional Edition
 * Microsoft Visual C++ 1.5 Professional Edition
 * Microsoft Visual C++ 2.0 Professional Edition
 * Microsoft Visual C++ 4.0 Standard Edition
 * Microsoft Visual C++ 4.1 Subscription
 * Microsoft Visual C++ 4.2 Enterprise Edition
 * Microsoft Visual C++ 5.0 Enterprise Edition
 * Microsoft Visual C++ 6.0 Enterprise Edition
 * Microsoft Visual C++ 4.2 Professional Edition
 * Microsoft Visual C++ 5.0 Professional Edition
 * Microsoft Visual C++ 6.0 Professional Edition
 * Microsoft Visual C++ 6.0 Standard Edition

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This article was previously published under Q121888



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



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: kbprb kbcpponly kbcompiler KB121888

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