When can we use 'explicit' keyword..?

The keyword explicit is used to avoid implicit conversion. In case of implicit conversion we can initialise an object (with one argument) of a class using a constant. This is illustrated in the following program.

class sample
{

private :

int i ;

public :

sample ( int ii )
{

i = ii ;

}

} ;

void fun ( sample s )
{

// code

}

void main( )
{

fun ( 11 ) ; // implicit conversion

}

Here, we have passed integer 11 to fun( ) which would initialize s.i with 11. This is called implicit conversion. We use keyword explicit to avoid this implicit conversion. This keyword is a declaration specifier which can be used only with inline constructors. When a constructor is defined with this keyword, it indicates that the constructor cannot take part in implicit conversion. Thus, explicit conversion forces to initialize an object of a class with an object of the same class. As multiple-argument constructor cannot take part in implicit conversion, explicit can only be used with one-argument constructor. The following program illustrates use of explicit keyword.

class sample
{

private :

int i ;

public :

explicit sample ( int ii )
{

i = ii ;

}

} ;

void fun ( sample s )
{

// code

}

void main( )
{

sample s ( 9 ) ;
fun ( 11 ) ; // error
fun ( s ) ; // explicit conversion

}