PracticeDev/study_cpp/cpp_primer_source_code/Chapter 14/tmp2tmp.cpp

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2022-12-20 17:31:11 +08:00
// tmp2tmp.cpp -- template friends to a template class
#include <iostream>
using std::cout;
using std::endl;
// template prototypes
template <typename T> void counts();
template <typename T> void report(T &);
// template class
template <typename TT>
class HasFriendT
{
private:
TT item;
static int ct;
public:
HasFriendT(const TT & i) : item(i) {ct++;}
~HasFriendT() { ct--; }
friend void counts<TT>();
friend void report<>(HasFriendT<TT> &);
};
template <typename T>
int HasFriendT<T>::ct = 0;
// template friend functions definitions
template <typename T>
void counts()
{
cout << "template size: " << sizeof(HasFriendT<T>) << "; ";
cout << "template counts(): " << HasFriendT<T>::ct << endl;
}
template <typename T>
void report(T & hf)
{
cout << hf.item << endl;
}
int main()
{
counts<int>();
HasFriendT<int> hfi1(10);
HasFriendT<int> hfi2(20);
HasFriendT<double> hfdb(10.5);
report(hfi1); // generate report(HasFriendT<int> &)
report(hfi2); // generate report(HasFriendT<int> &)
report(hfdb); // generate report(HasFriendT<double> &)
cout << "counts<int>() output:\n";
counts<int>();
cout << "counts<double>() output:\n";
counts<double>();
// std::cin.get();
return 0;
}