HP C/aC++ for PA-RISC Software manual Classic example of this problem is an array class

explicit C(int);

};

C::C(int)

{

// empty definition

}

int main()

{

C	c(5);	//	Legal
c	= C(10);	//	Legal

//c = 15; // Produces a compile time error:

//Message: Cannot assign ‘C’ with ‘int’.

//c + 20; // Produces a compile time error

}

A classic example of this problem is an array class:

class Vector	{
public:
Vector(int	n);	// create a vector of n items

// other class details omitted

};

int main()

{

Vector operator + (Vector, Vector);

Vector v1(10), v2(10); // create two 10 element vectors

//	details omitted
v1	= v2 + 5;	// Legal - converts int 5		to	a 5
		// element vector and adds to v2.
		//	Not something you want	to	be
		//	legal

}

With the explicit keyword, the constructor can be made explicit and the declarations are legal, but the addition is a compilation error:

class Vector { public:

explicit Vector(int n); // create a vector of n items

// other class details omitted

};

int main()

{

Vector operator + (Vector, Vector);

Vector v1(10), v2(10); // create two 10 element vectors

//details omitted

//v1 = v2 + 5; // Not legal - generates compile-

//time error

//Message: Illegal typEs

//associated with operator ‘+’:

//‘Vector’ and ‘int’.

}

142 Standardizing Your Code