Share via


Outline of Changes (C++/CLI)

This outline shows you examples of some of the changes in the language from Managed Extensions for C++ to Visual C++. Follow the link that accompanies each item for more information.

No Double Underscore Keywords

The double underscore in front of all keywords has been removed, with one exception. Thus, __value becomes value, and __interface becomes interface, and so on. To prevent name clashes between keywords and identifiers in user code, keywords are primarily treated as contextual.

See Language Keywords (C++/CLI) for more information.

Class Declarations

Managed Extensions syntax:

__gc class Block {};                           // reference class
__value class Vector {};                       // value class
__interface I {};                        // interface class
__gc __abstract class Shape {};                // abstract class
__gc __sealed class Shape2D : public Shape {}; // derived class

New syntax:

ref class Block {};                // reference class
value class Vector {};             // value class
interface class I {};        // interface class
ref class Shape abstract {};       // abstract class
ref class Shape2D sealed: Shape{}; // derived class

See Managed Types (C++/CL) for more information.

Object Declaration

Managed Extensions syntax:

public __gc class Form1 : public System::Windows::Forms::Form {
private:
   System::ComponentModel::Container __gc *components;
   System::Windows::Forms::Button   __gc *button1;
   System::Windows::Forms::DataGrid __gc *myDataGrid;   
   System::Data::DataSet  __gc *myDataSet;
};

New syntax:

public ref class Form1 : System::Windows::Forms::Form {
   System::ComponentModel::Container^ components;
   System::Windows::Forms::Button^ button1;
   System::Windows::Forms::DataGrid^ myDataGrid;
   System::Data::DataSet^ myDataSet;
};

See Declaration of a CLR Reference Class Object for more information.

Managed Heap Allocation

Managed Extensions syntax:

Button* button1 = new Button; // managed heap
int *pi1 = new int;           // native heap
Int32 *pi2 = new Int32;       // managed heap

New syntax:

Button^ button1 = gcnew Button;        // managed heap
int * pi1 = new int;                   // native heap
Int32^ pi2 = gcnew Int32;              // managed heap

See Declaration of a CLR Reference Class Object for more information.

A Tracking Reference to No Object

Managed Extensions syntax:

// OK: we set obj to refer to no object
Object * obj = 0;

// Error: no implicit boxing
Object * obj2 = 1;

New syntax:

// Incorrect Translation
// causes the implicit boxing of both 0 and 1
Object ^ obj = 0;
Object ^ obj2 = 1;

// Correct Translation
// OK: we set obj to refer to no object
Object ^ obj = nullptr;

// OK: we initialize obj2 to an Int32^
Object ^ obj2 = 1;

See Declaration of a CLR Reference Class Object for more information.

Array Declaration

The CLR array has been redesigned. It is similar to the stl vector template collection, but maps to the underlying System::Array class – that is, it is not a template implementation.

See Declaration of a CLR Array for more information.

Array as Parameter

Managed Extensions array syntax:

void PrintValues( Object* myArr __gc[]); 
void PrintValues( int myArr __gc[,,]); 

New array syntax:

void PrintValues( array<Object^>^ myArr );
void PrintValues( array<int,3>^ myArr );

Array as Return Type

Managed Extensions array syntax:

Int32 f() []; 
int GetArray() __gc[];

New array syntax:

array<Int32>^ f();
array<int>^ GetArray();

Shorthand Initialization of Local CLR Array

Managed Extensions array syntax:

int GetArray() __gc[] {
   int a1 __gc[] = { 1, 2, 3, 4, 5 };
   Object* myObjArray __gc[] = { __box(26), __box(27), __box(28),
                                 __box(29), __box(30) };

   return a1;
}

New array syntax:

array<int>^ GetArray() {
   array<int>^ a1 = {1,2,3,4,5};
   array<Object^>^ myObjArray = {26,27,28,29,30};

   return a1;
}

Explicit CLR Array Declaration

Managed Extensions array syntax:

Object* myArray[] = new Object*[2];
String* myMat[,] = new String*[4,4];

New array syntax:

array<Object^>^ myArray = gcnew array<Object^>(2);
array<String^,2>^ myMat = gcnew array<String^,2>(4,4);

New to language: explicit array initialization that follows gcnew

// explicit initialization list follow gcnew 
// is not supported in Managed Extensions
array<Object^>^ myArray = 
   gcnew array<Object^>(4){ 1, 1, 2, 3 };

Scalar Properties

Managed Extensions property syntax:

public __gc __sealed class Vector {
   double _x;

public:
   __property double get_x(){ return _x; }
   __property void set_x( double newx ){ _x = newx; }
};

New property syntax:

public ref class Vector sealed { 
   double _x;

public:
   property double x 
   {
      double get()             { return _x; }
      void   set( double newx ){ _x = newx; }
   } // Note: no semi-colon …
};

New to language: trivial properties

public ref class Vector sealed { 
public:
   // equivalent shorthand property syntax
   // backing store is not accessible
   property double x; 
};

See Property Declaration for more information.

Indexed Properties

Managed Extensions indexed property syntax:

public __gc class Matrix {
   float mat[,];

public: 
   __property void set_Item( int r, int c, float value) { mat[r,c] = value; }
   __property int get_Item( int r, int c ) { return mat[r,c]; }
};

New indexed property syntax:

public ref class Matrix {
   array<float, 2>^ mat;

public:
   property float Item [int,int] {
      float get( int r, int c ) { return mat[r,c]; }
      void set( int r, int c, float value ) { mat[r,c] = value; }
   }
};

New to language: class-level indexed property

public ref class Matrix {
   array<float, 2>^ mat;

public:
   // ok: class level indexer now
   //     Matrix mat;
   //     mat[ 0, 0 ] = 1; 
   //
   // invokes the set accessor of the default indexer

   property float default [int,int] {
      float get( int r, int c ) { return mat[r,c]; }
      void set( int r, int c, float value ) { mat[r,c] = value; }
   }
};

See Property Index Declaration for more information.

Overloaded Operators

Managed Extensions operator overload syntax:

public __gc __sealed class Vector {
public:
   Vector( double x, double y, double z );

   static bool    op_Equality( const Vector*, const Vector* );
   static Vector* op_Division( const Vector*, double );
};

int main() {
   Vector *pa = new Vector( 0.231, 2.4745, 0.023 );
   Vector *pb = new Vector( 1.475, 4.8916, -1.23 ); 

   Vector *pc = Vector::op_Division( pa, 4.8916 );

   if ( Vector::op_Equality( pa, pc ))
      ;
}

New operator overload syntax:

public ref class Vector sealed {
public:
   Vector( double x, double y, double z );

   static bool    operator ==( const Vector^, const Vector^ );
   static Vector^ operator /( const Vector^, double );
};

int main() {
   Vector^ pa = gcnew Vector( 0.231, 2.4745, 0.023 );
   Vector^ pb = gcnew Vector( 1.475, 4.8916, -1.23 );

   Vector^ pc = pa / 4.8916;
   if ( pc == pa )
      ;
}

See Overloaded Operators for more information.

Conversion Operators

Managed Extensions conversion operator syntax:

__gc struct MyDouble {
   static MyDouble* op_Implicit( int i ); 
   static int op_Explicit( MyDouble* val );
   static String* op_Explicit( MyDouble* val ); 
};

New conversion operator syntax:

ref struct MyDouble {
public:
   static operator MyDouble^ ( int i );
   static explicit operator int ( MyDouble^ val );
   static explicit operator String^ ( MyDouble^ val );
};

See Changes to Conversion Operators for more information.

Explicit Override of an Interface Member

Managed Extensions explicit override syntax:

public __gc class R : public ICloneable {
   // to be used through ICloneable
   Object* ICloneable::Clone();

   // to be used through an R
   R* Clone();
};

New explicit override syntax:

public ref class R : public ICloneable {
   // to be used through ICloneable
   virtual Object^ InterfaceClone() = ICloneable::Clone;

   // to be used through an R 
   virtual R^ Clone();
};

See Explicit Override of an Interface Member for more information.

Private Virtual Functions

Managed Extensions private virtual function syntax:

__gc class Base {
private:
   // inaccessible to a derived class
   virtual void g(); 
};

__gc class Derived : public Base {
public:
   // ok: g() overrides Base::g()
   virtual void g();
};

New private virtual function syntax

ref class Base {
private:
   // inaccessible to a derived class
   virtual void g(); 
};

ref class Derived : public Base {
public:
   // error: cannot override: Base::g() is inaccessible
   virtual void g() override;
};

See Private Virtual Functions for more information.

CLR Enum Type

Managed Extensions enum syntax:

__value enum e1 { fail, pass };
public __value enum e2 : unsigned short  { 
   not_ok = 1024, 
   maybe, ok = 2048 
};  

New enum syntax:

enum class e1 { fail, pass };
public enum class e2 : unsigned short { 
   not_ok = 1024,
   maybe, ok = 2048 
};

Apart from this small syntactic change, the behavior of the CLR enum type has been changed in a number of ways:

  • A forward declaration of a CLR enum is no longer supported.

  • The overload resolution between the built-in arithmetic types and the Object class hierarchy has reversed between Managed Extensions and Visual C++. As a side-effect, CLR enums are no longer implicitly converted to arithmetic types.

  • In the new syntax, a CLR enum maintains its own scope, which is not the case in Managed Extensions. Previously, enumerators were visible within the containing scope of the enum; now, enumerators are encapsulated within the scope of the enum.

See CLR Enum Type for more information.

Removal of __box Keyword

Managed Extensions boxing syntax:

Object *o = __box( 1024 ); // explicit boxing

New boxing syntax:

Object ^o = 1024; // implicit boxing

See A Tracking Handle to a Boxed Value for more information.

Pinning Pointer

Managed Extensions pinning pointer syntax:

__gc struct H { int j; };

int main() {
   H * h = new H;
   int __pin * k = & h -> j;
};

New pinning pointer syntax:

ref struct H { int j; };

int main() {
   H^ h = gcnew H;
   pin_ptr<int> k = &h->j;
}

See Value Type Semantics for more information.

__typeof Keyword becomes typeid

Managed Extensions typeof syntax:

Array* myIntArray = 
   Array::CreateInstance( __typeof(Int32), 5 );

New typeid syntax:

Array^ myIntArray = 
   Array::CreateInstance( Int32::typeid, 5 );

See typeof Goes to T::typeid for more information.

See Also

Concepts

C++/CLI Migration Primer

Component Extensions for Runtime Platforms

Other Resources

Managed Extensions for C++ Syntax Upgrade Checklist