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std::ios_base::precision

From cppreference.com
< cpp‎ | io‎ | 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.

Contents

[edit] Parameters

new_precision - new precision setting

[edit] Return value

The precision before the call to the function

[edit] Example

#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

[edit] 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

[edit] See also

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