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__sealed

Visual Studio .NET 2003

Prevents a method from being overridden or a class from being a base class.

__sealed class-specifier
__sealed struct-specifier
__sealed function-declarator

Remarks

The __sealed keyword specifies that a class method cannot be overridden or that a class cannot be a base class.

When using the __sealed keyword, keep the following points in mind:

  • A __sealed virtual method cannot be overridden.
  • If a nonvirtual member method is marked __sealed, the __sealed qualification is ignored.
  • A __sealed method cannot be pure.
  • The __sealed keyword is not allowed when used with the __interface keyword.

When a class (or struct) is marked with __sealed, the class cannot be used as a base class. For example:

__sealed __gc class A
{
   // ...
};
// error: cannot derive from a sealed class
__gc class B : public A { /* ...*/ };
Note   The __sealed keyword is not allowed when used with the __abstract keyword.

Example

In the following example, a sealed virtual method (f) is declared. The function is then overridden in main(), causing a compiler error:

// keyword__sealed.cpp
// compile with: /clr
#using <mscorlib.dll>
extern "C" int printf(const char*, ...);

__gc struct I
{
   __sealed virtual void f() { printf("I::f()\n"); }
   virtual void g() { printf("I::g()\n"); }
};

__gc struct A : I
{
   void f() { printf("A::f()\n"); }  // C3248, can't override a sealed function
   void g() { printf("A::g()\n"); }
};

int main()
{
   A* pA = new A;
   pA->f();
   pA->g();
   return 0;
}

See Also

Managed Extensions for C++ Reference | C++ Keywords

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