Compiler Error C3450

'type': not an attribute; cannot specify [System::AttributeUsageAttribute] or [Windows::Foundation::Metadata::AttributeUsageAttribute]

Remarks

A user-defined managed attribute must inherit from AttributeCollection. A Windows Runtime attribute must be defined in the Windows::Foundation::Metadata namespace.

For more information, see User-Defined Attributes.

Example

The following example generates C3450 and shows how to fix it.

// C3450.cpp
// compile with: /clr
// C3450 expected
using namespace System;
using namespace System::Security;
using namespace System::Security::Permissions;

public ref class MyClass {};

class MyClass2 {};

[attribute(AttributeTargets::All)]
ref struct AtClass {
   AtClass(Type ^) {}
};

[attribute(AttributeTargets::All)]
ref struct AtClass2 {
   AtClass2() {}
};

// Apply the AtClass and AtClass2 attributes to class B
[AtClass(MyClass::typeid), AtClass2]
[AttributeUsage(AttributeTargets::All)]
// Delete the following line to resolve.
ref class B {};
// Uncomment the following line to resolve.
// ref class B : Attribute {};