newbie question about constructor

[sam]

Hi,
Why declare constructors implicit or explicit ,whats the use of it?

 

[wittempj]

Hi,
Why declare constructors implicit or explicit ,whats the use of it?

See http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.1

 

[Rolf Magnus]

Hi,
Why declare constructors implicit or explicit ,whats the use of it?

Constructors that can be called with one argument are conversion
constructors. If the constructor is not declared 'explicit', the compiler
will do implicit conversions using that constructor.

struct X{};
struct Y{};

class MyClass
{
public:
MyClass(X);
explicit MyClass(Y);
};

void myfunc(MyClass);

int main()
{
X x;
Y y;

myfunc(x); // ok, conversion constructor is implicitly used
myfunc(y); // error, constructor is explicit
myfunc(static_cast<MyClass>(y)); // ok, explicit conversion
}

Btw: What C++ book are you reading that doesn't explain this?