C/C++编程：字符串输入输出流stringstream

小咪咪 2022-05-18 06:24 296阅读 0赞

> # std::[stringstream][] #
> 
>     typedef basic_stringstream<char> stringstream;
> 
> Input/output string stream
> 
> ![202103031135264.png][]
> 
> 流类对字符串进行操作
> 
> 这是一个basci\_stringstream的示例，具有以下模板参数
> 
> <table> 
>  <tbody> 
>   <tr> 
>    <th>template parameter</th> 
>    <th>definition</th> 
>    <th>comments</th> 
>   </tr> 
>   <tr> 
>    <td>charT</td> 
>    <td><code>char</code></td> 
>    <td>成员char_type的别名</td> 
>   </tr> 
>   <tr> 
>    <td>traits</td> 
>    <td><code><a href="http://www.cplusplus.com/char_traits" rel="nofollow">char_traits</a>&lt;char&gt;</code></td> 
>    <td>成员traits_type的别名</td> 
>   </tr> 
>   <tr> 
>    <td>Alloc</td> 
>    <td><code><a href="http://www.cplusplus.com/allocator" rel="nofollow">allocator</a>&lt;char&gt;</code></td> 
>    <td>成员&nbsp;allocator_type的别名</td> 
>   </tr> 
>  </tbody> 
> </table>

##  ##

## std::[stringstream][]::stringstream ##

// swapping ostringstream objects
    #include <string>       // std::string
    #include <iostream>     // std::cout
    #include <sstream>      // std::stringstream
    
    int main () {
    
        std::stringstream ss;
    
        ss << 100 << ' ' << 200;
    
        int foo,bar;
        ss >> foo >> bar;
    
        std::cout << "foo: " << foo << '\n';
        std::cout << "bar: " << bar << '\n';
    
        return 0;
    }

![20210303113401998.png][]

# std :: [stringstream][] :: str #

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

// stringstream::str
    #include <string>       // std::string
    #include <iostream>     // std::cout
    #include <sstream>      // std::stringstream, std::stringbuf
    
    int main () {
      std::stringstream ss;
      ss.str ("Example string");
      std::string s = ss.str();
      std::cout << s << '\n';
      return 0;
    }

![20210303113814706.png][]

## std::[ios][]::good、std :: [ios][] :: fail、**std::[ios][]::bad** ##

>     bool good() const;
> 
> 作用：检查流状态是否良好
> 
> 该函数的行为就像定义为：
> 
>     bool ios::good() const {
>       return rdstate() == goodbit;
>     }
> 
> 返回值：
> 
>  *  `true` 如果未设置任何流的状态标志
>  *  `false` 如果设置了任何流的状态标志 (badbit, eofbit or failbit).
> 
> > 可以使用成员函数[eof][]，[fail][]，[bad][] 检查是否设置了特定的错误标志
> > 
> > <table> 
> >  <tbody> 
> >   <tr> 
> >    <th><a href="http://www.cplusplus.com/ios_base::iostate" rel="nofollow">iostate</a>&nbsp;value<br> (member constant)</th> 
> >    <th>表示</th> 
> >    <th colspan="5">检查状态标志的功能</th> 
> >   </tr> 
> >   <tr> 
> >    <th><a href="http://www.cplusplus.com/ios::good" rel="nofollow">good()</a></th> 
> >    <th><a href="http://www.cplusplus.com/ios::eof" rel="nofollow">eof()</a></th> 
> >    <th><a href="http://www.cplusplus.com/ios::fail" rel="nofollow">fail()</a></th> 
> >    <th><a href="http://www.cplusplus.com/ios::bad" rel="nofollow">bad()</a></th> 
> >    <th><a href="http://www.cplusplus.com/ios::rdstate" rel="nofollow">rdstate()</a></th> 
> >   </tr> 
> >   <tr> 
> >    <th>goodbit</th> 
> >    <td>No errors (zero value&nbsp;<a href="http://www.cplusplus.com/ios_base::iostate" rel="nofollow">iostate</a>)</td> 
> >    <td><code>true</code></td> 
> >    <td><code>false</code></td> 
> >    <td><code>false</code></td> 
> >    <td><code>false</code></td> 
> >    <td>goodbit</td> 
> >   </tr> 
> >   <tr> 
> >    <th>eofbit</th> 
> >    <td>输入操作到达文件末尾</td> 
> >    <td><code>false</code></td> 
> >    <td><code>true</code></td> 
> >    <td><code>false</code></td> 
> >    <td><code>false</code></td> 
> >    <td>eofbit</td> 
> >   </tr> 
> >   <tr> 
> >    <th>failbit</th> 
> >    <td> <p>I / O操作上的逻辑错误</p> </td> 
> >    <td><code>false</code></td> 
> >    <td><code>false</code></td> 
> >    <td><code>true</code></td> 
> >    <td><code>false</code></td> 
> >    <td>failbit</td> 
> >   </tr> 
> >   <tr> 
> >    <th>badbit</th> 
> >    <td>I / O操作中的读/写错误</td> 
> >    <td><code>false</code></td> 
> >    <td><code>false</code></td> 
> >    <td><code>true</code></td> 
> >    <td><code>true</code></td> 
> >    <td>badbit、</td> 
> >   </tr> 
> >  </tbody> 
> > </table>
> 
> > **std :: [ios][] :: fail**
> > 
> >     bool fail（）const;
> > 
> > 作用：检查是否设置了故障位或故障位
> > 
> > 当输入操作期间发生错误时，将至少设置这些标志中的一个。
> > 
> > **std::[ios][]::bad**
> > 
> >     bool bad() const;
> > 
> > 作用：检查是否设置了badbit
> > 
> > 当在读取或写入数据时发生错误时，通常通过对流执行的操作来设置此标志，这通常会导致流完整性的损失

#include <iostream>     // std::cout, std::ios
    #include <sstream>      // std::stringstream
    
    void print_state (const std::ios& stream) {
        std::cout << " good()=" << stream.good();
        std::cout << " eof()=" << stream.eof();
        std::cout << " fail()=" << stream.fail();
        std::cout << " bad()=" << stream.bad();
    }
    int main () {
        std::stringstream stream;
    
        stream.clear (stream.goodbit);
        std::cout << "goodbit:"; print_state(stream); std::cout << '\n';
    
        stream.clear (stream.eofbit);
        std::cout << " eofbit:"; print_state(stream); std::cout << '\n';
    
        stream.clear (stream.failbit);
        std::cout << "failbit:"; print_state(stream); std::cout << '\n';
    
        stream.clear (stream.badbit);
        std::cout << " badbit:"; print_state(stream); std::cout << '\n';
        
        return 0;
    }

![20210303114827785.png][]

##       \--- ##

[stringstream]: http://www.cplusplus.com/reference/sstream/stringstream/
[202103031135264.png]: /images/20220518/f8ec3765a8c84b09af718b04f23195a4.png
[20210303113401998.png]: /images/20220518/5bfbad04186b4dafb4d36d39b638288e.png
[20210303113814706.png]: /images/20220518/62687a2f6ef7406188b1ff5b03f07712.png
[ios]: http://www.cplusplus.com/reference/ios/ios/
[eof]: http://www.cplusplus.com/ios::eof
[fail]: http://www.cplusplus.com/ios::fail
[bad]: http://www.cplusplus.com/ios::bad
[20210303114827785.png]: /images/20220518/7844c6e930ed4e7f97ae65ae0bfd1524.png