Hello again. I am stuck with this example:
#define Listof(Type) class Type##List \
{ \
public: \
Type##List(){} \
private: \
int itsLength; \
};
could anyone explain to me what is the intention and the point in this example? beacause I found this example in a book but not explained.
Where did this come from? I have not seen coding like this, at all.
It's old school templating before C++ supported (or widely supported) templates. I'd question how old your book is if that's an example. It must be at least 20 years old. Regardless, not a book you should be learning modern C++ from unless that example is prefixed, suffixed, and bordered with "DO NOT DO THIS".
That is an absolutely terrible example, it should never appear in a book, or at least, not one worth reading (unless it is presented as an example of what not to do).
In any case, what this MACRO is trying to do is automatically generate a list of objects of a particular type. For example, if you have some class called Foo and you use that MACRO as Listof(Foo), it will expand to this:
class FooList
{
public:
FooList(){}
private:
int itsLength;
};
Or, I imagine there was more to it than that, but you get the point, it generates a complete declaration of a class FooList to represent a list of Foo objects.
In reality, C++ has a native feature for this kind of thing, it is called templates. You would normally write this instead:
template <typename T>
class List {
public:
List(){}
private:
int itsLength;
};
and then use it as List<Foo>. This is how standard containers like std::vector and std::list are made.
Any book that recommends or shows this MACRO technique is either extremely old and written by a grossly incompetent programmer.
Hello Guys! I forgot to tell you that this book just explained the CONCATENATION operator and it is exlpaining the preference of TEMPLATES rather than MACRO. what I want now: after you create FooList, do you mean that Foo is another class??? if so how could you use and initialize its objects in FooList??? for example I have 5 objects of type Foo how to manage them in FooList???? Any help is highly appreciated.
Note: i just want to know how could I make the example work
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