Question

How to print a double value with full precision using cout in C++

Answer 1

#include <iostream>
 
int main() {
    double f = 3.141592653589793;
    
    std::cout.unsetf(std::ios::floatfield);             
    std::cout.precision(16);
    std::cout << f << "\n";
 
    std::cout.precision(14);
    std::cout << f << "\n";
   
    std::cout.setf(std::ios::fixed, std:: ios::floatfield); 
    std::cout << f << '\n';
}

  
  
/*
run:
  
3.141592653589793
3.1415926535898
3.14159265358979
 
*/
    

 

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Answer 2

#include <iostream>
#include <iomanip>

int main() {
    std::cout << std::setprecision(16) << 3.141592653589793 << std::endl;
}

    
          
/*
run:
       
3.141592653589793

*/

 

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Answer 3

#include <iostream>
#include <numbers>
#include <format>
 
int main()
{
    std::cout << std::format("{}", std::numbers::pi_v<double>); // C++ 20
}
 
 
/*
run:

3.141592653589793 

*/

 

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