C ++：在ofstream文件中写一个双近似值，例如printf（“％f…）

Question

I have this problem. I get the result from the function double sin(double x) of the library cmath. I want to write this result in a file declared as ofstream file and I want that when the result is close to zero, write 0.000000 and not 1.22465e-16 . For example, I tried:

`double x=sin(interval*c);
 file<<"value:"<<x;
 printf("value:%f",x);`

where the multiplication between interval and c is about π.

But in the file is written 1.22465e-16 , while in the shell is written 0.000000 . How can i do to get the approximation 0.000000 in ofstream file? Thanks all

Answer 1

If you want the same format the "%f" specifier uses (rather than the default which is "%g" ), you'd use

std::cout << std::fixed;

To restore the original format, ie, get back to using the same format as "%g" you'd use

std::cout << std::defaultfloat; // C++11
std::cout.setf(std::ios_base::fmtflags(), std::ios_base::floatfield); // pre C++11

Answer 2

您可以检查它是否低于阈值并将其设置为0

 if(fabs(x) < 1e-8) x = 0;