C++中類模板(class template) 詳解

類模板(class template)需要添加模板參數(template parameter), 即最前面添加"template <template T>";

把所有需要使用模板類型的位置, 使用"T"代替; 使用時需要填加"Class<T>",指定模板參數;

在定義類的成員函數(member function)時, 也需要添加類的模板參數"template <template T>",

並且在聲明函數的歸屬類時, 類需要轉換為模板類, 即"Class::"轉換為"Class<T>::";

如果在類中, 如果使用本類對象, 即當前對象, 則可以不添加模板參數(添加也不沒有問題);

其餘注意初始化列表"initializer_list"的用法, 和首碼++或--與尾碼++或--在重載時的區別;

代碼如下:

/*  * cppprimer.cpp  *  *  Created on: 2013.11.21  *      Author: Caroline  */      /*eclipse cdt, gcc 4.8.1*/      #include <iostream>  #include <vector>  #include <initializer_list>  #include <memory>  #include <cstddef>        template <typename T> class BlobPtr;  template <typename T> class Blob;        /*Blob: Binary Large OBject*/template <typename T> class Blob {      friend class BlobPtr<T>;  public:      typedef T value_type;      typedef typename std::vector<T>::size_type size_type;      Blob ();      Blob (std::initializer_list<T> il); //可以使用初始化列表, {}      size_type size() const { return data->size(); }      bool empty() const { return data->empty(); }      void push_back (const T &t) { data->push_back(t); }      void push_back (T &&t) { data->push_back(std::move(t)); } //右值操作      void pop_back ();      T& back ();      T& operator[] (size_type i) ;  private:      std::shared_ptr<std::vector<T> > data;      void check (size_type i, const std::string &msg) const; //驗證給定的索引  };        template <typename T>  Blob<T>::Blob () : data(std::make_shared<std::vector<T>>()) {}        template <typename T>  Blob<T>::Blob (std::initializer_list<T> il) :          data(std::make_shared< std::vector<T> >(il)) {}        /*驗證給定的索引*/template <typename T>  void Blob<T>::check (size_type i, const std::string &msg) const{      if (i >= data->size())          throw std::out_of_range (msg); //拋出異常  }        template <typename T>  T& Blob<T>::back ()  {      check (0, "back on empty Blob");      return data->back ();  }        template <typename T>  T& Blob<T>::operator[] (size_type i)  {      check (i, "subscript out of range");      return (*data)[i];  }        template <typename T>  void Blob<T>::pop_back ()  {      check (0, "pop_back on empty Blob");      data->pob_back ();  }        template <typename T>  class BlobPtr {  public:      BlobPtr () : curr (0) {}      BlobPtr (Blob<T> &a, size_t sz=0) : wptr(a.data), curr (sz) {}      T& operator* () const {          auto p = check (curr, "dereference past end");          return (*p) [curr];      }      BlobPtr& operator++ (); //首碼操作符      BlobPtr& operator-- ();      BlobPtr operator++ (int); //尾碼操作符      BlobPtr operator-- (int);  private:      std::shared_ptr<std::vector<T>> check (std::size_t, const std::string&) const;      std::weak_ptr<std::vector<T>> wptr;      std::size_t curr;  };        template <typename T>  std::shared_ptr<std::vector<T>>  BlobPtr<T>::check (std::size_t i, const std::string& msg) const{      auto ret = wptr.lock (); //判斷wptr是否綁定了Blob      if (!ret)          throw std::runtime_error ("unbound BlobPtr");      if (i >= ret->size ())          throw std::out_of_range (msg);      return ret;  }        template <typename T>  BlobPtr<T>& BlobPtr<T>::operator++ () {      check (curr, "increment past end of BlobPtr"); //先判斷後加      ++curr;      return *this;  }        template <typename T>  BlobPtr<T>& BlobPtr<T>::operator-- () {      --curr; //先減之後, 如果為0, 再減就是大整數      check (curr, "decrement past begin of BlobPtr"); //先減後判斷      return *this;  }        template <typename T>  BlobPtr<T> BlobPtr<T>::operator ++(int)  {      BlobPtr ret = *this;      ++*this; //使用重載的首碼++      return ret;  }        template <typename T>  BlobPtr<T> BlobPtr<T>::operator --(int)  {      BlobPtr ret = *this;      --*this; //使用重載的首碼--      return ret;  }        int main (void) {      std::cout << "Hello Mystra!" << std::endl;      Blob<int> ia;      Blob<int> ia2 = {0, 1, 2, 3, 4};      std::cout << "ia2[2] = " << ia2[2] << std::endl;      BlobPtr<int> pia = ia2;      std::cout << "*(++pia) = " << *(++pia) << std::endl;      return 0;  }

作者：csdn部落格 Spike_King

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