The use of explicit with constructor

[utab]

Dear all,

Can experienced users clarify the use of explicit keyword for ctors
with some examples?

Regards,

[Noah Roberts]

utab wrote:

Dear all,

Can experienced users clarify the use of explicit keyword for ctors
with some examples?

Regards,

class MagicInt
{
int x;
public:
MagicInt(int i) : x(i) {}
};

class ExplicitMagicInt
{
int x;
public:
explicit ExplicitMagicInt(int i) : x (i) {}
};

int main(void)
{
MagicInt i1(5);
ExplicitMagicInt i2(5);
MagicInt i3 = 5;
ExplicitMagicInt i4 = 5;

return 0;
}

[Alan Johnson]

utab wrote:

Dear all,

Can experienced users clarify the use of explicit keyword for ctors
with some examples?

Regards,

class A
{
public:
A(int x) : x_(x)
{}

int get_x() { return x_ ; }
private:
int x_ ;
} ;

int f(A a)
{
return a.get_x() ;
}

int main()
{
// Fine, class A can be implicitly constructed from an int.
A a1 = 5 ;

// Fine, class A can be implicitly constructed from an int.
f(3);
}
If you change class A's construct to be explicit, then A cannot be
implicitly constructed from an int, and both lines in main become errors.

--
Alan Johnson