extending a class

[Mathes]

Hello,

i have a question about extending a class.

class ExString : public std::string {...};

now i want to implement some constructors.

i had this two:

ExString::ExString(const std::string &old)
: std::string(old)
{ }

ExString::ExString(const ExString &old)
: std::string(static_cast<std::string>(old))
{ }

then i removed the second one and my unit test of the copy constructor with an ExString-object still succeeds.

...
ExString es3("Cat");
ExString es4(es3);
BOOST_CHECK_EQUAL(es4 == es3, true);
...

so my question is:
when my class derives one other class, is it enough to implement the copy constructor for an argument of the base class?

i would say yes (at least in this case), but im not sure.

Regards,
Mathes

[jsmith]

The compiler gives you a default copy constructor that does a member-wise copy.

You shouldn't derive from std::string, however, as std::string is not meant to be a base class (ie, no virtual destructor).

[Mathes]

thanks for your answer.