std::ios_base::precision

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std::ios_base
 
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 = 1.2345678901234;
    std::cout << "The  default precision is " << std::cout.precision() << "\n\n";
    std::cout << "With default precision d is " << d << '\n';
    std::cout.precision(12);
    std::cout << "With high    precision d is " << d << '\n';
}

Output: 

The  default precision is 6
 
With default precision d is 1.23457
With high    precision d is 1.23456789012

Defect reports

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

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

See also

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