C/C++编程：std::cin、std::cout

本是古典何须时尚 2022-05-20 02:13 173阅读 0赞

# std :: [ios\_base][ios_base] :: flags #

> 作用：**获取/设置格式标志**

// modify flags
    #include <iostream>     // std::cout, std::ios
    
    int main () {
      std::cout.flags ( std::ios::right | std::ios::hex | std::ios::showbase );
      std::cout.width (10);
      std::cout << 100 << '\n';
      return 0;
    }

![20210303130930231.png][]

# std :: [ios\_base][ios_base] :: setf、std::[ios\_base][ios_base]::unsetf #

> **(1) setf：设置特定的格式标志**
> 
> (2) unsetf：清除特定格式的标志

// modifying flags with setf/unsetf
    #include <iostream>     // std::cout, std::ios
    
    int main () {
      std::cout.setf ( std::ios::hex, std::ios::basefield );  // set hex as the basefield
      std::cout.setf ( std::ios::showbase );                  // activate showbase
      std::cout << 100 << '\n';
      std::cout.unsetf ( std::ios::showbase );                // deactivate showbase
      std::cout << 100 << '\n';
      return 0;
    }

![20210303131523132.png][]

# std::[ios\_base][ios_base]::precision #

> 作用：获取/设置浮点十进制精度

// modify precision
    #include <iostream>     // std::cout, std::ios
    
    int main () {
      double f = 3.14159;
      std::cout.unsetf ( std::ios::floatfield );                // floatfield not set
      std::cout.precision(5);
      std::cout << f << '\n';
      std::cout.precision(10);
      std::cout << f << '\n';
      std::cout.setf( std::ios::fixed, std:: ios::floatfield ); // floatfield set to fixed
      std::cout << f << '\n';
      return 0;
    }

![20210303131930548.png][]

# std::[ios\_base][ios_base]::width #

> 作用：获取/设置字段宽度

// field width
    #include <iostream>     // std::cout, std::left
    
    int main () {
        std::cout << 100 << '\n';
        std::cout.width(10);
        std::cout << 100 << '\n';
        std::cout.fill('x');
        std::cout.width(15);
        std::cout << std::left << 100 << '\n';
        return 0;
    }

![20210303132202918.png][]

# std :: [ios\_base][ios_base] :: imbue #

> 作用：设置语言环境（locale）

// imbue example
    #include <iostream>     // std::cout
    #include <locale>       // std::locale
    
    int main()
    {
      std::locale mylocale("");   // get global locale
      std::cout.imbue(mylocale);  // imbue global locale
      std::cout << 3.14159 << '\n';
      return 0;
    }

![2021030313242371.png][]

# std :: [ios\_base][ios_base] :: sync\_with\_stdio #

> 作用：设置每个输入输出操作后是否将标准C++流同步到标准C流

#include <iostream>
    #include <cstdio>
     
    int main()
    {
        std::ios::sync_with_stdio(false);
        std::cout << "a\n";
        std::printf("b\n");
        std::cout << "c\n";
    }

![20210303133913208.png][]

#  #

\----

[ios_base]: http://www.cplusplus.com/reference/ios/ios_base/
[20210303130930231.png]: /images/20220520/54de30dcceeb4d32a155a09c7916f0ca.png
[20210303131523132.png]: /images/20220520/e9324fa0ef404f51b33747df5dfe3f87.png
[20210303131930548.png]: /images/20220520/fc8784316ed64251913456a501eb8ac1.png
[20210303132202918.png]: /images/20220520/8401d76881b5471bb0d74cc3944e02b3.png
[2021030313242371.png]: /images/20220520/dcbf0bc9ec574e3fb14e85cc1bba049b.png
[20210303133913208.png]: /images/20220520/fe2dae4e46a04b41b1c417216237577c.png