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const_cast Operator

Removes the const, volatile, and __unaligned attribute(s) from a class.


const_cast < type-id > ( expression )

A pointer to any object type or a pointer to a data member can be explicitly converted to a type that is identical except for the const, volatile, and __unaligned qualifiers. For pointers and references, the result will refer to the original object. For pointers to data members, the result will refer to the same member as the original (uncast) pointer to data member. Depending on the type of the referenced object, a write operation through the resulting pointer, reference, or pointer to data member might produce undefined behavior.

You cannot use the const_cast operator to directly override a constant variable's constant status.

The const_cast operator converts a null pointer value to the null pointer value of the destination type.

// expre_const_cast_Operator.cpp
// compile with: /EHsc
#include <iostream>

using namespace std;
class CCTest {
public:
   void setNumber( int );
   void printNumber() const;
private:
   int number;
};

void CCTest::setNumber( int num ) { number = num; }

void CCTest::printNumber() const {
   cout << "\nBefore: " << number;
   const_cast< CCTest * >( this )->number--;
   cout << "\nAfter: " << number;
}

int main() {
   CCTest X;
   X.setNumber( 8 );
   X.printNumber();
}

On the line containing the const_cast, the data type of the this pointer is const CCTest *. The const_cast operator changes the data type of the this pointer to CCTest *, allowing the member number to be modified. The cast lasts only for the remainder of the line on which it appears.

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