C++语法基础--泛型算法（generic algorithm)--iostream迭代器

╰+哭是因爲堅強的太久メ 2022-01-10 07:07 238阅读 0赞

**\*流迭代器只定义了最基本的迭代器操作：自增，解引用和赋值  
\*可以比较两个istream迭代器是否相等（或不等）  
\*ostream迭代器则不能提供比较运算  
  
  
  
  
1.iostream的构造函数  
![20130713000935687][]  
  
原型：  
 default ：istream\_iterator();  
initialization ：istream\_iterator (istream\_type& s);  
copy ：istream\_iterator (const istream\_iterator& x);  
解析：  
default constructor：  
Constructs an end-of-stream istream iterator.  
initalization constructor：  
Constructs an istream iterator that is associated with stream s  
(the object does not own or copy the stream, only stores a reference).  
  
  
copy constructor：  
Constructs an istream iterator, with the same istream reference and current value  
(it does not attempt to extract an additional element on construction).  
  
  
\*istream\_iterator的操作  
![20130713001004718][]  
  
  
  
Example:  
 int main ()  
\{  
std::istream\_iterator<double> eos;  // end-of-stream iterator  
 std::istream\_iterator<double> iit (cin);  // read doubles from cin  
  
  
 while(iit!=eos)  
 \{   
 cout<<\*iit<<' ';//逐个提取流中的数据  
 iit++;  
 \}  
  
  
 return 0;  
\}  
  
  
  
  
  
  
  
2.ostream\_iterator  
构造函数：  
initialization ：  
ostream\_iterator (ostream\_type& s);  
ostream\_iterator (ostream\_type& s, const char\_type\* delimiter);  
copy :  
ostream\_iterator (const ostream\_iterator& x);  
  
解析：  
 delimiter必须是C风格字符串  
  
  
Example:  
 int main()  
\{**

**ostream\_iterator<int> i1(std::cout, ", "); //定义一个ostream\_iterator对象，**

**//用于将int类型的数据写到cout中，每个int后跟一个","**

**fill\_n(i1, 3, -1);//-1 -1 -1  
  
 ostream\_iterator<double> i2(std::cout);  
 for(int i=0;i<3;i++)  
\{   
\*i2++=i;//012  
\}  
\}  
  
  
Tips:  
一旦给ostream\_iterator对象赋值，写入就提交了，赋值后，没有办法再改变这个值  
  
  
  
  
3.在类类型上使用ostream\_iterator,istream\_iterator  
\*提供了输入操作符<<的任何类型都可以创建ostream\_iterator对象  
\*提供了输入操作符>>的任何类型都可以创建istream\_iterator对象  
  
Example:  
class A  
 \{   
 public:  
A(int i):x(i)\{\}  
friend ostream& operator<<(ostream &os,A b);  
 private:  
int x;  
\};  
  
  
 ostream& operator<<(ostream &os,A b)  
 \{   
os<<b.x;  
return os;  
 \}  
  
  
int main()  
\{   
 ostream\_iterator<A> i1(std::cout,",");  
 \*i1=A(2);  
\*i1=A(3);  
\}  
  
  
  
  
output:2,3,  
  
  
  
  
4.与算法一起使用流迭代器  
Example:  
int main(void)  
\{  
istream\_iterator<int> beg(cin); //假设输入1,2,3,2,1,3  
istream\_iterator<int> end;  
vector<int> vec(beg,end);  
sort(vec.begin(),vec.end());  
ostream\_iterator<int> os(cout);  
unique\_copy(vec.begin(),vec.end(),os); //输出123  
  
  
 return 0;  
\}**

[20130713000935687]: /images/20220109/0dc04d93d87b407b81adf0628d6ef2d3.png
[20130713001004718]: /images/20220109/3005972c116b41daac4c8499eda678ab.png