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std::setprecision(3) C++ Standard Libary std::setprecision(3) NAME std::setprecision - std::setprecision Synopsis Defined in header <iomanip> /*unspecified*/ setprecision( int n ); When used in an expression out << setprecision(n) or in >> setpreci- sion(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 <iomanip> #include <iostream> #include <limits> #include <numbers> int main() { constexpr long double pi{std::numbers::pi_v<long double>}; const auto default_precision{std::cout.precision()}; constexpr auto max_precision{std::numeric_limits<long dou- ble>::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 de- faults } 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 Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Cor- rect behavior LWG 183 C++98 setprecision could only be used with streams us- able with any of type std::ostream or std::istream character stream See also fixed scientific hexfloat changes formatting used for floating-point I/O defaultfloat (function) (C++11) (C++11) precision manages decimal precision of floating point operations (public member function of std::ios_base) http://cppreference.com 2024.06.10 std::setprecision(3)
NAME | Synopsis | Parameters | Return value | Example | Output: | See also
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