问题
I've got a large set of inherited classes (criteria) which inherit from a base class (criterion). Here's criterion
's code
class criterion
{
public:
virtual unsigned __int32 getPriorityClass() const = 0;
virtual BOOL include(fileData &file) const = 0;
virtual void reorderTree() = 0;
virtual unsigned int directoryCheck(const std::wstring& directory) const = 0;
virtual std::wstring debugTree() const = 0;
};
Some examples of derived classes from this one:
class fastFilter : public criterion
{
public:
void reorderTree() {};
unsigned int directoryCheck(const std::wstring& /*directory*/) const { return DIRECTORY_DONTCARE; };
unsigned __int32 getPriorityClass() const { return PRIORITY_FAST_FILTER; };
};
class isArchive : public fastFilter
{
public:
BOOL include(fileData &file) const
{
return file.getArchive();
}
std::wstring debugTree() const
{
return std::wstring(L"+ ISARCHIVE\n");
};
};
Since I don't have a destructor here at all, but yet this is supposed to be a base class, do I need to insert an empty virtual destructor, I.e. like this?:
virtual void ~criterion() = 0;
If that virtual destructor declaration is needed, do all intermediate classes need one as well? I.e. would fastFilter above need a virtual destructor as well?
回答1:
Yes - the base class needs a virtual destructor, even if it's empty. If that is not done, then when something delete
's a derived object through a base pointer/reference, the derived object's member objects will not get a chance to destroy themselves properly.
Derived classes do not need to declare or define their own destructor unless they need something other than default destructor behavior.
回答2:
The recommendation is to insert
virtual ~criterion() {}
to avoid the deletion off a base class pointer problem. Otherwise you will leak memory as derived classes' destructors will not be called.
criterion *c = new fastFilter();
delete c; // leaks
回答3:
You don't need to make the destructor abstract, just give it a empty implementation:
virtual ~criterion() { }
This way you are not forced to implement it in every child class, but still each of them will have a (inherited) virtual destructor.
回答4:
One small change from what others have already answered:
Instead of
virtual void ~criterion() = 0;
the required version is:
virtual ~criterion() {} //Note: Removed void as destructors not allowed
// a return type
To know more about virtual destructor have a look at this link from FAQ When should my destructor be virtual?
来源:https://stackoverflow.com/questions/827196/virtual-default-destructors-in-c