In fact you already wrote all. Only instead of struct structName
I would use const struct structName &
myClass::myClass( const structName &s )
{
someVar = s.someOtherVar;
}
Or you could define the constructor as
myClass::myClass( const structName &s ) : someVar( s.someOtherVar )
{
}
In this declaration
myClass(struct structName);
struct structName
is so-called elaborated type name. It introduces a new type in the namespace where the class is defined.
In your example you at first declared the structure and then defined it. The constructor declaration does not require that the structure would be a complete type.