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.
Warning
This topic refers to the C++ Component Extensions version of typeid. For the ISO C++ version of this keyword, see typeid Operator.
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