I've been reading (and using the examples in) Thinking in C++ (vol 2).
One of the things that the author shows you can do with templates is
the following:
#include <iostream>
using namespace std;
template<class T>
class Counted
{
static int count;
public:
Counted() { ++count; }
Counted(const Counted<T>&) { ++count; }
~Counted() { --count; }
static int getCount() { return count; }
};
template<class T>
int Counted<T>::cou nt = 0;
// Curious class definitions
class CountedClass : public Counted<Counted Class> {};
class CountedClass2 : public Counted<Counted Class2> {};
int main()
{
CountedClass a;
cout << CountedClass::g etCount() << endl; // 1
CountedClass b;
cout << CountedClass::g etCount() << endl; // 2
CountedClass2 c;
cout << CountedClass2:: getCount() << endl; // 1 (!)
} ///:~
I've tried adapting this idea to the following class that I've
used/created to try out some other things (Below is the almost working
example).
Header file:
[code]
#ifndef ID_CLASS_H
#define ID_CLASS_H
#include <map>
// magic number defines
#define NOT_A_VALID_ID -1
template<class T>
class ID_Class
{
private:
static std::map<int, int> ID_Map;
int ID_Value;
void DecrementRefere nce();
void IncrementRefere nce();
public:
// Only reason to ever NOT use the default constructor is when you
read
// the IDs from a source instead of creating new IDs.
ID_Class(int tID);
ID_Class();
~ID_Class();
ID_Class(const ID_Class<T>& Right);
ID_Class<T>& operator= (const ID_Class<T>& Right);
int Get_ID() const;
// Test/debug functions below this comment
void DumpMap() const;
};
#endif
cpp:
#include "ID_Class.h "
#include <stdexcept>
#include <ostream>
// note that #include <map> has been defined in the header. This is
needed
// for the static definition used there.
using std::cout;
using std::overflow_e rror;
using std::bad_alloc;
using std::pair;
using std::map;
template<class T>
map<int, int> ID_Class<T>::ID _Map;
// private functions
template<class T>
void ID_Class<T>::De crementReferenc e()
{
map<int,int>::i terator it = ID_Map.find(ID_ Value);
--(it->second);
if ( it->second < 1)
{
ID_Map.erase(it );
}
}
template<class T>
void ID_Class<T>::In crementReferenc e()
{
map<int,int>::i terator it = ID_Map.find(ID_ Value);
++(it->second);
if (it->second < 1)
{
throw overflow_error( "To many copies exist");
}
}
// public functions
template<class T>
ID_Class<T>::ID _Class(int tID)
{
ID_Value = tID;
if ((ID_Map.insert (pair<int,int>( ID_Value,1))).s econd == false)
{
throw bad_alloc();
}
}
template<class T>
ID_Class<T>::ID _Class()
{
ID_Value = 1;
map<int,int>::c onst_iterator it (ID_Map.begin() );
map<int,int>::c onst_iterator itEnd (ID_Map.end());
while(( it != itEnd) && (ID_Value == (*it).first))
{
++ID_Value;
++it;
}
if (ID_Value < 1)
{
throw overflow_error( "Requested negative ID");
}
if ((ID_Map.insert (pair<int,int>( ID_Value,1))).s econd == false)
{
throw bad_alloc();
}
}
template<class T>
ID_Class<T>::~I D_Class()
{
DecrementRefere nce();
}
template<class T>
ID_Class<T>::ID _Class(const ID_Class<T>& Right)
{
ID_Value = Right.ID_Value;
IncrementRefere nce();
}
template<class T>
ID_Class<T>& ID_Class<T>::op erator= (const ID_Class<T>& Right)
{
DecrementRefere nce();
ID_Value = Right.ID_Value;
IncrementRefere nce();
return *this;
}
template<class T>
int ID_Class<T>::Ge t_ID() const
{
return ID_Value;
}
// Test/Debug functions below this comment
template<class T>
void ID_Class<T>::Du mpMap() const
{
map<int,int>::c onst_iterator it (ID_Map.begin() );
map<int,int>::c onst_iterator itEnd (ID_Map.end());
while (it != itEnd)
{
cout << "ID " << (*it).first << " Has " << (*it).second << " copies"
<< endl;
++it;
}
}
main.cpp:
#include "ID_Class.h "
#include <iostream>
using namespace std
class MainID : public ID_Class<MainID >
{
};
int main( int argc, char* argv[])
{
// MainID TestID;
char t;
cin.get(t);
return(0);
};
I know that I'm missing something here since the code will compile
without a warning but when I uncomment // Main TestID; I get
unresolved externals (ctor & dtor). The question is what is is that am
I missing? What rules am I trying to break? And is there a way around
the problem? 4 1504
"velthuijse n" <ve*********@ho tmail.com> wrote in message
news:e5******** *************** ***@posting.goo gle.com... I've been reading (and using the examples in) Thinking in C++ (vol 2).
One of the things that the author shows you can do with templates is the following:
[snip] I know that I'm missing something here since the code will compile without a warning but when I uncomment // Main TestID; I get unresolved externals (ctor & dtor). The question is what is is that am I missing? What rules am I trying to break? And is there a way around the problem?
It's the old, old problem. Put all your template code in the header file,
that's where it belongs. I'm surprised Bruce Eckel didn't explain that in
his book, but here it is in the FAQ. http://www.parashift.com/c++-faq-lit...templates.html
questions 34.12 to 34.15
john
"velthuijse n" <ve*********@ho tmail.com> wrote in message
news:e5******** *************** ***@posting.goo gle.com... I've been reading (and using the examples in) Thinking in C++ (vol 2).
One of the things that the author shows you can do with templates is the following:
[snip] I know that I'm missing something here since the code will compile without a warning but when I uncomment // Main TestID; I get unresolved externals (ctor & dtor). The question is what is is that am I missing? What rules am I trying to break? And is there a way around the problem?
It's the old, old problem. Put all your template code in the header file,
that's where it belongs. I'm surprised Bruce Eckel didn't explain that in
his book, but here it is in the FAQ. http://www.parashift.com/c++-faq-lit...templates.html
questions 34.12 to 34.15
john
"John Harrison" <jo************ *@hotmail.com> wrote in message news:<c4******* ******@ID-196037.news.uni-berlin.de>... "velthuijse n" <ve*********@ho tmail.com> wrote in message news:e5******** *************** ***@posting.goo gle.com... I've been reading (and using the examples in) Thinking in C++ (vol 2).
One of the things that the author shows you can do with templates is the following: [snip] I know that I'm missing something here since the code will compile without a warning but when I uncomment // Main TestID; I get unresolved externals (ctor & dtor). The question is what is is that am I missing? What rules am I trying to break? And is there a way around the problem?
It's the old, old problem. Put all your template code in the header file, that's where it belongs. I'm surprised Bruce Eckel didn't explain that in his book, but here it is in the FAQ.
He did. In his first book, chapter 16. Guess this is what I get when I
just copy/paste existing files instead of trying to remember all the
excercises he'd suggested. http://www.parashift.com/c++-faq-lit...templates.html
questions 34.12 to 34.15
"John Harrison" <jo************ *@hotmail.com> wrote in message news:<c4******* ******@ID-196037.news.uni-berlin.de>... "velthuijse n" <ve*********@ho tmail.com> wrote in message news:e5******** *************** ***@posting.goo gle.com... I've been reading (and using the examples in) Thinking in C++ (vol 2).
One of the things that the author shows you can do with templates is the following: [snip] I know that I'm missing something here since the code will compile without a warning but when I uncomment // Main TestID; I get unresolved externals (ctor & dtor). The question is what is is that am I missing? What rules am I trying to break? And is there a way around the problem?
It's the old, old problem. Put all your template code in the header file, that's where it belongs. I'm surprised Bruce Eckel didn't explain that in his book, but here it is in the FAQ.
He did. In his first book, chapter 16. Guess this is what I get when I
just copy/paste existing files instead of trying to remember all the
excercises he'd suggested. http://www.parashift.com/c++-faq-lit...templates.html
questions 34.12 to 34.15 This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
by: papi1976 |
last post by:
Hello to everyone
I heard about a strange thing about wich i have'nt find anything on the net
or
books, someone called this "Curiously recursive pattern" or a strange trick
to play with templates and inheritance...
Dunno what is that or how it works :(
Does someone has any idea about this thing???
|
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last post by:
The following code does not compile
template <class Derived>
struct X
{
typedef typename Derived::type type;
};
struct Y : public X<Y>
{
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by: velthuijsen |
last post by:
I've been reading (and using the examples in) Thinking in C++ (vol 2).
One of the things that the author shows you can do with templates is
the following:
#include <iostream>
using namespace std;
template<class T>
class Counted
|
by: iuweriur |
last post by:
A few questions on the curiously recurring template pattern:
This page:
http://c2.com/cgi/wiki?CuriouslyRecurringTemplate
this part:
template<typename T> struct ArithmeticType
{
T operator + (const T& other) const
{
|
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Hi Gang,
The following code does not compile, but I can't figure out why. The
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Is there any way of making the code work? I would like functions to
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"value_type" of the function that it is "curiously calling".
Thanks.
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