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Guest · Posted: Fri May 12, 2006 12:21 pm Post subject: derived class init

Hi,

I have some legacy code looks like this:

class Tool
{
public:
Tool(char* name);

virtual void do();
};

class Work
{
private:
Tool _tool;

public:
Work();

void run();
}

The Work.cc is defined as:

Work::Work()
:
_tool("Old Tool")
{
....
}

void Work::run(){
....
_tool.do();
....
}

And some other code is using class Work.

Now I have a NewTool class:

class NewTool : public Tool
{
public:
NewTool(char* name);

virtual void do()
{
my new do...
}
}

I would like to use my NewTool in Work. But some old code is not
compatible with NewTool. So I have to keep Work class as it is and I
deceided to define a NewWork class derived from Work. All I want is to
give "_tool" a NewTool object. I want to keep code change as minimum
as possible and prefer not to change Tool or Work. But if I have to
change them, it is OK too.

class NewWork : public Work
{
public:
NewWork();
}

I am wondering how I can write the constructor of NewWork so that is
has all function from Work but uses NewTool. The following code does
not work:

NewWork::NewWork
:
_tool(NewTool("New Tool"))
{
}

Can anyone help?

Thanks,

qq

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Manfred von Willich · Guest

You are creating class NewWork, which contains class Work (as a base
class), which contains a member of class Tool. You cannot initialise a
member of a base class in the initializer list of the derived class -
Work's constructor will already have done this before the initializers
run.