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Important This document may not represent best practices for current development, links to downloads and other resources may no longer be valid. Current recommended version can be found here.

C-Style Casts with /clr

When used with CLR types, the compiler attempts to map C-style cast to one of the casts listed below, in the following order:

  1. const_cast

  2. safe_cast

  3. safe_cast plus const_cast

  4. static_cast

  5. static_cast plus const_cast

If none of the casts listed above is valid, and if the type of the expression and the target type are CLR reference types, C-style cast maps to a runtime-check (castclass MSIL instruction). Otherwise, a C-style cast is considered invalid and the compiler issues an error.

A C-style cast is not recommended. When compiling with /clr (Common Language Runtime Compilation), use safe_cast.

The following sample shows a C-style cast that maps to a const_cast.

// cstyle_casts_1.cpp
// compile with: /clr
using namespace System;

ref struct R {};
int main() {
   const R^ constrefR = gcnew R();
   R^ nonconstR = (R^)(constrefR); 
}

The following sample shows a C-style cast that maps to a safe_cast.

// cstyle_casts_2.cpp
// compile with: /clr
using namespace System;
int main() {
   Object ^ o = "hello";
   String ^ s = (String^)o;
}

The following sample shows a C-style cast that maps to a safe_cast plus const_cast.

// cstyle_casts_3.cpp
// compile with: /clr
using namespace System;

ref struct R {};
ref struct R2 : public R {};

int main() {
   const R^ constR2 = gcnew R2();
   try {
   R2^ b2DR = (R2^)(constR2);
   }
   catch(InvalidCastException^ e) {
      System::Console::WriteLine("Invalid Exception");
   }
}

The following sample shows a C-style cast that maps to a static_cast.

// cstyle_casts_4.cpp
// compile with: /clr
using namespace System;

struct N1 {};
struct N2 {
   operator N1() {
      return N1();
   }
};

int main() {
   N2 n2;
   N1 n1 ;
   n1 = (N1)n2;
}

The following sample shows a C-style cast that maps to a static_cast plus const_cast.

// cstyle_casts_5.cpp
// compile with: /clr
using namespace System;
struct N1 {};

struct N2 {
   operator const N1*() {
      static const N1 n1;
      return &n1;
   }
};

int main() {
   N2 n2;
   N1* n1 = (N1*)(const N1*)n2;   // const_cast + static_cast
}

The following sample shows a C-style cast that maps to a run-time check.

// cstyle_casts_6.cpp
// compile with: /clr
using namespace System;

ref class R1 {};
ref class R2 {};

int main() {
   R1^ r  = gcnew R1();
   try {
      R2^ rr = ( R2^)(r);
   }
   catch(System::InvalidCastException^ e) {
      Console::WriteLine("Caught expected exception");
   }
}

The following sample shows an invalid C-style cast, which causes the compiler to issue an error.

// cstyle_casts_7.cpp
// compile with: /clr
using namespace System;
int main() {
   String^s = S"hello";
   int i = (int)s;   // C2440
}

Compiler option: /clr

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