std::ios_base::precision

• Using the default floating-point notation, the precision field specifies the maximum number of meaningful digits to display in total counting both those before and those after the decimal point. Notice that it is not a minimum, and therefore it does not pad the displayed number with trailing zeros if the number can be displayed with less digits than the precision.
• In both the fixed and scientific notations, the precision field specifies exactly how many digits to display after the decimal point, even if this includes trailing decimal zeros. The digits before the decimal point are not relevant for the precision in this case.

Parameters

prec

New value for the floating-point precision.
streamsize is a signed integral value.

Return Value

Example

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// 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;
}

3.1416
3.14159
3.1415900000

Data races

Exception safety

See also

setprecision

Set decimal precision (function)

ios_base::width

Get/set field width (public member function)

ios_base::setf

Set specific format flags (public member function)