模板类中的成员函数定义返回值为类中的typedef类型时候注意

找了好就终于找到错误原因。

 

如果模板类中的成员要访问类中的typedef类型必须加上关键字typename来指明它是一个类型。

 

如一下代码中的那个成员函数size。

 

#include <iostream>#include <string>template<typename Type>class List{public:typedef unsigned size_type;public:List();void push_back(const Type &value);void push_front(const Type &value);Type& front() const;Type& back() const;size_type size() const;~List();private:struct DataType{Type Value;struct DataType *next;}head;struct DataType *end;};template<typename Type>List<Type>::List(){head.next = 0;end = &head;}template<typename Type>void List<Type>::push_back(const Type &value){DataType *tmp = new DataType;tmp->Value = value;tmp->next = 0;end->next = tmp;end = tmp;}template<typename Type>void List<Type>::push_front(const Type &value){DataType *tmp = new DataType;tmp->Value = value;tmp->next = 0;tmp->next = head.next;head.next = tmp;}template<typename Type>Type& List<Type>::front() const{return head.next->Value;}template<typename Type>Type& List<Type>::back() const{return end->Value;}template<typename Type>typename List<Type>::size_type List<Type>::size() const{size_type iSize = 0;struct DataType *begin = &head;while (begin->next){++iSize;}return iSize;}template<typename Type>List<Type>::~List(){struct DataType *tmp = &head;while (tmp = tmp->next){head.next = tmp->next;free(tmp);tmp = &head;}}int main(){List<int> list;list.push_back(100);list.push_front(200);std::cout << list.front() << "/t" << list.back() << std::endl;system("pause");return 0;}