C++ iomanip setprecision()用法及代碼示例

C++中iomaip庫的setprecision()方法用於根據為此方法的參數指定的精度來設置ios庫浮點精度。

setprecision(int n)

參數：此方法接受n作為參數，該參數是要設置浮點精度的整數參數。返回值：此方法不返回任何內容。它僅用作流操縱器。示例1：

C++

// C++ code to demonstrate 
// the working of setprecision() function 
  
#include <iomanip> 
#include <ios> 
#include <iostream> 
  
using namespace std; 
  
int main() 
{ 
  
    // Initializing the decimal 
    double num = 3.142857142857; 
  
    cout << "Before setting the precision:\n"
         << num << endl; 
  
    // Using setprecision() 
    cout << "Setting the precision using"
         << " setprecision to 5:\n"
         << setprecision(5); 
  
    cout << num << endl; 
  
    // Using setprecision() 
    cout << "Setting the precision using
            "<<" setprecision to 9:\n " 
         << setprecision(9); 
  
    cout << num << endl; 
  
    return 0; 
}

輸出：

Before setting the precision:
3.14286
Setting the precision using setprecision to 5:
3.1429
Setting the precision using setprecision to 9:
3.14285714

範例2：

C++

// C++ code to demonstrate 
// the working of setprecision() function 
  
#include <iomanip> 
#include <ios> 
#include <iostream> 
  
using namespace std; 
  
int main() 
{ 
  
    // Initializing the decimal 
    double num = 3.14; 
  
    cout << fixed; 
  
    cout << "Before setting the precision:\n"
         << num << endl; 
  
    // Using setprecision() 
    cout << "Setting the precision using"
         << " setprecision to 5:\n"
         << setprecision(5); 
  
    cout << num << endl; 
  
    // Using setprecision() 
    cout << "Setting the precision using"
         << " setprecision to 9:\n"
         << setprecision(9); 
  
    cout << num << endl; 
    return 0; 
}

輸出：

Before setting the precision:
3.140000
Setting the precision using setprecision to 5:
3.14000
Setting the precision using setprecision to 9:
3.140000000

參考： http://www.cplusplus.com/reference/iomanip/setprecision/

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