对于使用类模板下的友员函数的使用注意

╰+攻爆jí腚メ 2022-08-10 11:47 47阅读 0赞

今天编了一个使用模板的数组

using namespace std;
 //class template Array
 template<typename T>
 class Array;
 template<typename T>ostream & operator <<(ostream & out,const Array<T>&aa);
 template<typename T>
 class Array{
 public:
 typedef typename list<T>::iterator iter;
 typedef typename list<T>::const_iterator const_iter;
 Array(){}//constructor
 Array(T array[],T count) {
 for (T i = 0; i < count; ++i) {
 MyArray.push_back( array [ i ] );
 } MyArray.unique( );
 }//constructor with index
 Array(const Array<T>& aa ) {
 if ( &aa == this ) return;
 MyArray.clear( );
 MyArray = aa.MyArray;
 }//copy constructor
 //function begin for iterator
 iter begin(){
 return MyArray.begin();
 }
 //function end for iterator
 iter end(){
 return MyArray.end();
 }
 //function begin for const_iterator
 const_iter begin()const{
 return ((const list<T>&)MyArray).begin();
 }
 //function end for const_iterator
 const_iter end()const{
 return ((const list<T>&)MyArray).end();
 }
 //overloading operator =
 Array<T>& operator =(const Array<T>& aa){
 if(&aa==this)return *this;
 MyArray.clear();
 MyArray=aa.MyArray;
 return *this;
 }
 friend ostream & operator <<(ostream & out,const Array<T>&aa){
 out<<"[";
 const_iter it=aa.begin();
 if(it!=aa.end()){
 out<<*it;
 
 if(it!=aa.end()){
 for(it++;it!=aa.end();it++)
 out<<","<<*it;
 }
 }
 out<<"]";
 return out;
 }
 
 private:
 
 list<T> MyArray;//container named MyArray
 
 };
 //Defined a class named A_iterator
 template<typename T>
 class A_iterator{
 public:
 
 A_iterator(){
 }//constructor
 
 A_iterator(typename list<T>::iterator it){
 this->it = it;
 }//construtor with index
 
 typename list<T>::iterator getIt() const{
 return it;
 }//function getIt
 
 T& operator*(){
 return *it;
 }//overloading operator *
 
 typename list<T>::iterator& operator++(){
 ++it;
 return it;
 }//overloading operator ++
 typename list<T>::iterator operator++(int){
 list<int>::iterator old = it;
 it++;
 return old;
 }//overloding operator ++ in back sequnce
 bool operator!=(const A_iterator& b){
 return it!=b.getIt();
 }//overloading operator !=
 bool operator==(const A_iterator& b){
 return it==b.getIt();
 }//overloding operator ==
 
 private:
 typename list<T>::iterator it;//container_iterator named MyArray
 };

之前在

friend ostream & operator <<(ostream & out,const Array<T>&aa)

这一句运行时老是出错，其解决的方式在于加上类似蓝色部分

<pre name="code" class="html">template<typename T>
 class Array;
 template<typename T>ostream & operator <<(ostream & out,const Array<T>&aa);

其中第一句是用来声明使用这个类型Array而之后一句则是用来对输出流重载时的一种模板下的定义。毕竟，不能再类内部定义模板函数。！！！！长知识了 ![大笑][laugh.gif]

[laugh.gif]: /images/20220810/fd02ff227bc24743b7d530a615827b59.png