C++语法基础--泛型算法（generic algorithm)--反向迭代器,reverse_iterator::base()

朱雀 2022-01-12 12:35 275阅读 0赞

**1.反向迭代器：反向遍历容器的迭代器（既从最后一个元素到第一个元素遍历容器）  
\*++运算将访问前一个元素  
\*--运算则访问下一个元素  
  
  
  
2.反向迭代器的类型  
\*reverse\_iterator  
\*const\_reverse\_iterator  
  
3.begin/end和rbegin/rend迭代器的比较  
![20130713233448078][]  
  
  
Example:  
 int main ()  
\{  
int myints\[\]=\{1,2,3,4,5\};  
vector<int> myvector (myints,myints+5);  
for(vector<int>::reverse\_iterator rit=myvector.rbegin();rit!=myvector.rend();rit++)  
\{  
 cout<<\*rit<<'\\t'; //5 4 3 2 1  
 \}  
  
 return 0;  
\}  
  
  
  
  
4.反向迭代器和泛型算法结合使用可以实现逆序操作的效果  
Example:  
 int main ()  
\{  
int myints\[\]=\{3,5,2,8,1\};  
vector<int> myvector (myints,myints+5);  
sort(myvector.rbegin(),myvector.rend());  
for(int x:myvector)  
\{  
 cout<<x<<'\\t'; //8 5 3 2 1  
 \}  
 return 0;  
\}  
  
  
Tips:  
\*标准容器上的迭代器既支持自增运算，也支持自减运算。  
\*流迭代器由于不能反向遍历，因此不能创建反向迭代器  
  
  
  
  
  
  
5.reverse\_iterator::base  
Returns a copy of the base iterator.  
The base iterator is an iterator of the same type as the one used to construct the reverse\_iterator, but pointing to the element next to the one the reverse\_iterator is currently pointing to (a reverse\_iterator has always an offset of -1 with respect to its base iterator).  
原型：  
iterator\_type base() const;  
  
  
Example:  
int main ()  
\{  
std::vector<int> myvector;  
for (int i=1; i<=5; i++) myvector.push\_back(i);// 1 2 3 4 5  
auto beg=myvector.rend().base(); //myvector.rend()指向1的前一个元素,myvector.rend().base()指向1  
 auto end=(++myvector.rbegin()).base();//等效于myvector.rbegin()  
 // ++myvector.rbegin()指向myvector.rbegin()的前一个元素   
 cout<<\*beg<<endl;//1  
 cout<<\*end<<endl;//5  
  
  
 return 0;**

**\}**

**图解：**

**![20130713233842875][]**

[20130713233448078]: /images/20220109/7004dec29da84abfaa3a0e1d858be609.png
[20130713233842875]: /images/20220109/9c4df76627da4dec98c3ab17b70b2482.png