NAME¶

std::ios_base::precision - std::ios_base::precision

Synopsis¶

streamsize precision() const; (1)
streamsize precision( streamsize new_precision ); (2)

Manages the precision (i.e. how many digits are generated) of floating point output
performed by std::num_put::do_put.

1) Returns the current precision.
2) Sets the precision to the given one. Returns the previous precision.

The default precision, as established by std::basic_ios::init, is 6.

Parameters¶

new_precision - new precision setting

Return value¶

The precision before the call to the function

Example¶

// Run this code

#include <iostream>

int main()
{
const double d = 12.345678901234;
std::cout << "The default precision is " << std::cout.precision() << "\n\n";
std::cout << "With default precision d is " << d << '\n';
std::cout.precision(8);
std::cout << "With high precision d is " << d << '\n';
}

Output:¶

The default precision is 6

With default precision d is 12.3457
With high precision d is 12.345679

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
'precision' was defined as 'the number of digits
LWG 189 C++98 after corrected
the decimal point', but it is not correct in
some cases

See also¶

width manages field width
(public member function)
setprecision changes floating-point precision
(function)