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Compiler Warning (level 2) C4099

Visual Studio 2010

'identifier' : type name first seen using 'objecttype1' now seen using 'objecttype2'

An object declared as a structure is defined as a class, or an object declared as a class is defined as a structure. The compiler uses the type given in the definition.

Example

The following sample generates C4099.

Copy

// C4099.cpp
// compile with: /W2 /c
struct A;
class A {};   // C4099, use different identifer or use same object type

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FAQ

Useless warning ?

I have a big problem with this warning: According to the C++ standard, a struct is no different from a class (except for default visibility, which only has some impact for the class definition), and the following code should compile with no warnings:
class T;
struct T;
class T {};

I know that, once upon a time, VC++6.0 used a different name mangling for classes and struct, which created some link-time problem. I don't know if this bug has been corrected, and the document associated with this warning does not explicit if it is related to this bug or not.

History

10/12/2010
Loïc Joly

10/12/2010
Loïc Joly