typeid (C++ Component Extensions)

The latest version of this topic can be found at typeid (C++ Component Extensions).

Gets a value that indicates the type of an object.

All Runtimes

Syntax

  
T::typeid  

Parameters

T
A type name.

Windows Runtime

Syntax

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

Parameters

T
A type name.

Remarks

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

Requirements

Compiler option: /ZW

Common Language Runtime

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.

Requirements

Compiler option: /clr

Examples

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  

See Also

Component Extensions for Runtime Platforms