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typeid (C++ Component Extensions)

Gets a value that indicates the type of an object.

Platform::Type^ type = T::typeid;

T

A type name.

In C++/CX, typeid returns a Platform::Type that is constructed from runtime type information.

Compiler option: /ZW

Syntax

type::typeid

Parameters

type

The name of a type (abstract declarator) for which you want the System::Type object.

Remarks

typeid is used to get the Type for a type at compile time.

typeid is similar to getting the System::Type for a type at run time using GetType or GetType. However, typeid only accepts a type name as a parameter. If you want to use an instance of a type to get its System::Type name, use GetType.

typeid must be able to evaluate a type name (type) at compile time, whereas GetType evaluates the type to return at run time.

typeid can take a native type name or common language runtime alias for the native type name; see .NET Framework Equivalents to C++ Native Types (C++/CLI) for more information.

typeid also works with native types, although it will still return a System::Type. To get a type_info structure, use typeid Operator.

typeid is the sucessor to __typeof in the previous /clr syntax.

Compiler option: /clr

Example

The following example compares the typeid keyword to the GetType() member.

// keyword__typeid.cpp
// compile with: /clr
using namespace System;

ref struct G {
   int i;
};

int main() {
   G ^ pG = gcnew G;
   Type ^ pType = pG->GetType();
   Type ^ pType2 = G::typeid;

   if (pType == pType2)
      Console::WriteLine("typeid and GetType returned the same System::Type");
   Console::WriteLine(G::typeid);

   typedef float* FloatPtr;
   Console::WriteLine(FloatPtr::typeid);
}

Output

typeid and GetType returned the same System::Type
G
System.Single*

Example

The following sample shows that a variable of type System::Type can be used to get the attributes on a type. It also shows that for some types, you will have to create a typedef to use typeid.

// keyword__typeid_2.cpp
// compile with: /clr
using namespace System;
using namespace System::Security;
using namespace System::Security::Permissions;

typedef int ^ handle_to_int;
typedef int * pointer_to_int;

public ref class MyClass {};

class MyClass2 {};

[attribute(AttributeTargets::All)]
ref class AtClass {
public:
   AtClass(Type ^) {
      Console::WriteLine("in AtClass Type ^ constructor");
   }
};

[attribute(AttributeTargets::All)]
ref class AtClass2 {
public:
   AtClass2() {
      Console::WriteLine("in AtClass2 constructor");
   }
};

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

int main() {
   Type ^ MyType = B::typeid;

   Console::WriteLine(MyType->IsClass);
   
   array<Object^>^ MyArray = MyType -> GetCustomAttributes(true);
   for (int i = 0 ; i < MyArray->Length ; i++ )
      Console::WriteLine(MyArray[i]);

   if (int::typeid != pointer_to_int::typeid)
      Console::WriteLine("int::typeid != pointer_to_int::typeid, as expected");

   if (int::typeid == handle_to_int::typeid)
      Console::WriteLine("int::typeid == handle_to_int::typeid, as expected");
}

Output

True
in AtClass2 constructor
in AtClass Type ^ constructor
AtClass2
System.AttributeUsageAttribute
AtClass
int::typeid != pointer_to_int::typeid, as expected
int::typeid == handle_to_int::typeid, as expected
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