Outline of Changes (C++/CLI)
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The latest version of this topic can be found at 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
C++/CLI Migration Primer
(NOTINBUILD)Managed Extensions for C++ Syntax Upgrade Checklist
Component Extensions for Runtime Platforms