Article ID: 116487
Article Last Modified on 7/5/2005
APPLIES TO
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 1.5 Professional Edition
- Microsoft Visual C++ 1.0 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 Professional Edition
- Microsoft Visual C++ 5.0 Standard Edition
- Microsoft Visual C++ 6.0 Service Pack 5
- Microsoft Visual C++ .NET 2002 Standard Edition
- Microsoft Visual C++ .NET 2003 Standard Edition
This article was previously published under Q116487
SYMPTOMS
Class A has a member function that converts an instance of class B to an instance of class A. Class B also has a member function that converts an instance of class B to an instance of class A. Therefore, when you assign an instance of class B to an instance of class A, the compiler could use both conversion methods, resulting in an ambiguity. However, the C/C++ compiler does not generate an error message in this situation, as demonstrated by the sample code in the "MORE INFORMATION" section, below.
STATUS
Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article.
MORE INFORMATION
You can use the following sample code to reproduce this problem:
Sample Code
/* Compile options needed: none */ #include <iostream.h> class B; class A { public: // This is the function the compiler // chooses to call. A(B&) { cout << "called A::A(B&)" << endl; } }; class B { public: operator A() // This function does not get called. { B b; cout << "called operator B::A()" << endl; return b; } }; void main() { B b; A a = b; // A(b) or b.operator A()? // The compiler should issue an // error here but instead chooses // to call A::A(B&). cout << "failed: should not compile- see ARM 12.3.2" << endl; }
REFERENCES
"The Annotated C++ Reference Manual" (ARM), Ellis and Stroustrup, Section 12.3.2, "Conversion Functions."
Additional query words: kbVC400bug 8.00 8.00c 9.00
Keywords: kbbug kbcpponly kbcompiler KB116487