std::setprecision

 

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showpointnoshowpoint setprecision	fixedscientifichexfloatdefaultfloat (C++11)(C++11)
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Defined in header <iomanip>
/*unspecified*/ setprecision( int n );

When used in an expression out << setprecision(n) or in >> setprecision(n), sets the precision parameter of the stream out or in to exactly n.

Parameters

n

-

new value for precision

Return value

An object of unspecified type such that

• if out is an object of type std::basic_ostream<CharT, Traits>, the expression out << setprecision(n)
  • has type std::basic_ostream<CharT, Traits>&
  • has value out
  • behaves as if it called f(out, n)
• if in is an object of type std::basic_istream<CharT, Traits>, the expression in >> setprecision(n)
  • has type std::basic_istream<CharT, Traits>&
  • has value in
  • behaves as if it called f(in, n)

where the function f is defined as:

void f(std::ios_base& str, int n)
{
    // set precision
    str.precision(n);
}

Example

Run this code

#include <iostream>
#include <iomanip>
#include <cmath>
#include <limits>
 
int main()
{
    const long double pi = std::acos(-1.L);
    std::cout << "default precision (6): " << pi << '\n'
              << "std::setprecision(10): " << std::setprecision(10) << pi << '\n'
              << "max precision:         "
              << std::setprecision(std::numeric_limits<long double>::digits10 + 1)
              << pi << '\n';
}

Output:

default precision (6): 3.14159
std::setprecision(10): 3.141592654
max precision:         3.141592653589793239

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 183	C++98	setprecision could only be used with streams of type std::ostream or std::istream	usable with any character stream

See also

fixedscientifichexfloatdefaultfloat (C++11)(C++11)	changes formatting used for floating-point I/O (function)
precision	manages decimal precision of floating point operations (public member function of std::ios_base)