std::ios_base::precision

 

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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
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

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