C/C++编程：输入字符串流basic_istringstream、istringstream

怼烎@ 2022-05-21 13:11 176阅读 0赞

> # basic\_istringstream #
> 
> 这是一个类模板
> 
>     template <class charT，// basic_istringstream :: char_type 
>                class traits = char_traits <charT>，// basic_istringstream :: traits_type 
>                class Alloc = allocator <charT> // basic_istringstream :: allocator_type 
>                > class basic_istringstream;
> 
> ![20210303100411699.png][]
> 
> ### 模板实例化 ###
> 
>  *  [istringstream][]：Input string stream (class )
>  *  [wistringstream][]：Input string stream (wide) (class )
> 
> 这些实例化在中声明 [<sstream>][sstream]。
> 
> ### Member types ###
> 
> The class declares the following member types:
> 
> <table> 
>  <tbody> 
>   <tr> 
>    <th>member type</th> 
>    <th>definition</th> 
>    <th>notes</th> 
>   </tr> 
>   <tr> 
>    <td>char_type</td> 
>    <td>第一个模板参数 (charT)</td> 
>    <td>&nbsp;</td> 
>   </tr> 
>   <tr> 
>    <td>traits_type</td> 
>    <td>第二个模板参数 (traits)</td> 
>    <td>defaults to:&nbsp;<code><a href="http://www.cplusplus.com/char_traits" rel="nofollow">char_traits</a>&lt;charT&gt;</code></td> 
>   </tr> 
>   <tr> 
>    <td>allocator_type</td> 
>    <td>第三个模板参数 (Alloc)</td> 
>    <td>defaults to:&nbsp;<code><a href="http://www.cplusplus.com/allocator" rel="nofollow">allocator</a>&lt;charT&gt;</code></td> 
>   </tr> 
>   <tr> 
>    <td>int_type</td> 
>    <td><code><a href="http://www.cplusplus.com/char_traits" rel="nofollow">traits_type</a>::int_type</code></td> 
>    <td>&nbsp;</td> 
>   </tr> 
>   <tr> 
>    <td>pos_type</td> 
>    <td><code><a href="http://www.cplusplus.com/char_traits" rel="nofollow">traits_type</a>::pos_type</code></td> 
>    <td>generally, the same as&nbsp;<a href="http://www.cplusplus.com/streampos" rel="nofollow">streampos</a></td> 
>   </tr> 
>   <tr> 
>    <td>off_type</td> 
>    <td><code><a href="http://www.cplusplus.com/char_traits" rel="nofollow">traits_type</a>::off_type</code></td> 
>    <td>generally, the same as&nbsp;<a href="http://www.cplusplus.com/streamoff" rel="nofollow">streamoff</a></td> 
>   </tr> 
>  </tbody> 
> </table>

# istringstream #

## 构造 ##

> <table> 
>  <tbody> 
>   <tr> 
>    <th>default (1)</th> 
>    <td> <pre>explicit istringstream (ios_base::openmode which = ios_base::in);
> </pre> </td> 
>   </tr> 
>   <tr> 
>    <th>initialization (2)</th> 
>    <td> <pre>explicit istringstream (const string&amp; str,
>                         ios_base::openmode which = ios_base::in);
> </pre> </td> 
>   </tr> 
>   <tr> 
>    <th>copy (3)</th> 
>    <td> <pre>istringstream (const istringstream&amp;) = delete;
> </pre> </td> 
>   </tr> 
>   <tr> 
>    <th>move (4)</th> 
>    <td> <pre>istringstream (istringstream&amp;&amp; x);</pre> </td> 
>   </tr> 
>  </tbody> 
> </table>
> 
> \--

// istringstream constructors.
    #include <iostream>     // std::cout
    #include <sstream>      // std::istringstream
    #include <string>       // std::string
    
    int main () {
    
      std::string stringvalues = "125 320 512 750 333";
      std::istringstream iss (stringvalues);
    
      for (int n=0; n<5; n++)
      {
        int val;
        iss >> val;
        std::cout << val*2 << '\n';
      }
    
      return 0;
    }

![2021030310194077.png][]

## std::istringstream::str ##

>     string str() const;
>     void str (const string& s);
> 
> 作用：获取/设置内容

// istringstream::str
    #include <string>       // std::string
    #include <iostream>     // std::cout
    #include <sstream>      // std::istringstream
    
    int main () {
        std::istringstream iss;
        std::string strvalues = "32 240 2 1450";
    
        iss.str (strvalues);
    
        for (int n=0; n<4; n++)
        {
            int val;
            iss  >> val;
            std::cout << val << '\n';
        }
        std::cout << "Finished writing the numbers in: ";
        std::cout << iss.str() << '\n';
        return 0;
    }

![20210303102406880.png][]

## std::istringstream::rdbuf ##

>     stringbuf * rdbuf（）const;
> 
> 作用：获取流缓冲区
> 
> 返回值：返回一个指向内部的指针 [Stringbuf][]对象，该对象在构造上与之关联。

// istringstream::rdbuf
    #include <string>       // std::string
    #include <iostream>     // std::cout
    #include <sstream>      // std::istringstream, std::stringbuf
    
    int main () {
        std::istringstream iss;
        std::stringbuf *pbuf = iss.rdbuf();
    
        // using stringbuf directly:
        pbuf->str("Example string");
    
        int size = pbuf->in_avail();
    
        while (pbuf->in_avail()>0)
            std::cout << static_cast<char>(pbuf->sbumpc());
    
        return 0;
    }

![20210303102924668.png][]

## std::istringstream::swap ##

>     void swap (istringstream& x);
> 
> \--

// swapping istringstream objects
    #include <string>       // std::string
    #include <iostream>     // std::cout
    #include <sstream>      // std::istringstream
    
    int main () {
    
      std::istringstream foo ("100");
      std::istringstream bar ("200");
    
      foo.swap(bar);
    
      int val;
    
      foo >> val; std::cout << "foo: " << val << '\n';
      bar >> val; std::cout << "bar: " << val << '\n';
    
      return 0;
    }

![20210303103048671.png][]

[20210303100411699.png]: /images/20220521/806fab5512bf45fa87bdcd9fc74e1ada.png
[istringstream]: http://www.cplusplus.com/reference/sstream/istringstream/
[wistringstream]: http://www.cplusplus.com/reference/sstream/wistringstream/
[sstream]: http://www.cplusplus.com/%3Csstream%3E
[2021030310194077.png]: /images/20220521/f180c65759b44a9da88375281dc83836.png
[20210303102406880.png]: /images/20220521/25024a71c8714c39aa01c281a4bca915.png
[Stringbuf]: http://www.cplusplus.com/stringbuf
[20210303102924668.png]: /images/20220521/8c568661cecc46bb8f615f72cd73faed.png
[20210303103048671.png]: /images/20220521/9b4e5839fa0b43d79c6a1db03c760ce4.png