std::setprecision - cppreference.com (original) (raw)

| | | | | ---------------------------------------- | | | | /*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.

[edit] Parameters

[edit] 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); }

[edit] Example

#include #include #include #include   int main() { constexpr long double pi{std:🔢:pi_v};   const auto default_precision{std::cout.precision()}; constexpr auto max_precision{std::numeric_limits::digits10 + 1};   std::cout << "default precision: " << default_precision << '\n' << "maximum precision: " << max_precision << "\n\n" "precision: pi:\n";   for (int p{0}; p <= max_precision; ++p) std::cout << std::setw(2) << p << " " << std::setprecision(p) << pi << '\n';   std::cout << std::setprecision(default_precision); // restore defaults }

Output:

default precision: 6 maximum precision: 19   precision: pi: 0 3 1 3 2 3.1 3 3.14 4 3.142 5 3.1416 6 3.14159 7 3.141593 8 3.1415927 9 3.14159265 10 3.141592654 11 3.1415926536 12 3.14159265359 13 3.14159265359 14 3.1415926535898 15 3.14159265358979 16 3.141592653589793 17 3.1415926535897932 18 3.14159265358979324 19 3.141592653589793239

[edit] Defect reports

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

[edit] See also