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.


n - new value for precision

Return value

Returns an object of unspecified type such that if str is the name of an output stream of type std::basic_ostream<CharT, Traits> or an input stream of type std::basic_istream<CharT, Traits>, then the expression str << setprecision(n) or str >> setprecision(n) behaves as if the following code was executed:



#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';


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

See also

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

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