From: Warren Young
Date: July 2 2008 12:01pm
Subject: Re: Derive a structure and use it with storein
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On Jul 2, 2008, at 3:56 AM, Lo=EFc Dardant wrote:

> class User : public database::User
> {
> public:
>    User(mysqlpp::sql_varchar a, mysqlpp::sql_varchar b, =20
> mysqlpp::sql_int c
> );
>    ~User();
>    void foo();
> };

In C++, if a derived class has a function with the same name as one in =20=

the base class, the derived class's versions always hide those in the =20=

base class.  Thus, your single ctor in the derived class hides these =20
ctors defined in the base SSQLS:

User();	// default ctor, needed by STL containers
User(const mysqlpp::Row& row); // what your error is about
User(const mysqlpp::sql_varchar& a); // for-comparison ctor

You need to define all of these in your derivative for it to be a true =20=

SSQLS.  Their implementation can be trivial: just call the base class =20=

ctors of the same signature, passing along the parameters directly.

Technically, the one ctor you do have hides a similar one in the base =20=

SSQLS: the full-initialization ctor takes its parameters by const =20
reference, not by value.  You should redefine your one existing ctor =20
like so:

User(const mysqlpp::sql_varchar& a, const mysqlpp::sql_varchar& b, =20
const mysqlpp::sql_int& c);

Failing to match this signature won't prevent good code from =20
compiling, but taking the parameters by reference is more efficient in =20=

the case of stringish data types.  And if you're going to take them by =20=

reference, making them const references is simply a matter of =20
correctness, since you aren't actually modifying the referents.=