类模板(class template) 详解 及 代码
本文地址: /caroline_wendy/article/details/16906827
类模板(class template)需要添加模板参数(template parameter), 即最前面添加"template <template T>";
把所有需要使用模板类型的位置,使用"T"代替; 使用时需要填加"Class<T>",指定模板参数;
在定义类的成员函数(member function)时, 也需要添加类的模板参数"template <template T>",
并且在声明函数的归属类时, 类需要转换为模板类, 即"Class::"转换为"Class<T>::";
如果在类中, 如果使用本类对象, 即当前对象, 则可以不添加模板参数(添加也不没有问题);
其余注意初始化列表"initializer_list"的用法, 和前缀++或--与后缀++或--在重载时的区别;
代码如下:
/* * cppprimer.cpp * * Created on: .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; //验证给定的索引 }; 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)) {} /*验证给定的索引*/ 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); //抛出异常 } 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++ (); //前缀操作符 BlobPtr& operator-- (); BlobPtr operator++ (int); //后缀操作符 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 (); //判断wptr是否绑定了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"); //先判断后加 ++curr; return *this; } template <typename T> BlobPtr<T>& BlobPtr<T>::operator-- () { --curr; //先减之后, 如果为0, 再减就是大整数 check (curr, "decrement past begin of BlobPtr"); //先减后判断 return *this; } template <typename T> BlobPtr<T> BlobPtr<T>::operator ++(int) { BlobPtr ret = *this; ++*this; //使用重载的前缀++ return ret; } template <typename T> BlobPtr<T> BlobPtr<T>::operator --(int) { BlobPtr ret = *this; --*this; //使用重载的前缀-- 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; }
