[C++] 浮点数格式化输出

C++格式化输出浮点数

 

#include <iostream>using std::cout;using std::endl;using std::fixed;using std::scientific;int main(){ double x = 0.001234567; double y = 1.946e9; cout << "Displayed in default format:" << endl << x << '/t' << y << endl; cout << "/nDisplayed in scientific format:" << endl << scientific << x << '/t' << y << endl; cout << "/nDisplayed in fixed format:" << endl << fixed << x << '/t' << y << endl; return 0;}

 

Displayed in default format:
0.00123457      1.946e+009

Displayed in scientific format:
1.234567e-003   1.946000e+009

Displayed in fixed format:
0.001235        1946000000.000000

 

#include <iostream.h>main(void){ float a=100100.0, b=0.08; cout.setf(ios::right|ios::scientific|ios::showpoint); cout.width(20); cout <<(-a*b); return 0;}

 

-8.008000e+003

 

#include <iostream>#include <iomanip>#include <limits>using std::cout;using std::endl;using std::setprecision;using std::numeric_limits;int main() { const double pi = 3.14; cout << endl; for(double radius = .2 ; radius <= 3.0 ; radius += .2) cout << "radius = " << setprecision(numeric_limits<double>::digits10 + 1) << std::scientific << radius<< " area = " << std::setw(10) << setprecision(6)<< std::fixed << pi * radius * radius << endl; return 0;}

 

radius = 2.0000000000000001e-001  area =   0.125600
radius = 4.0000000000000002e-001  area =   0.502400
radius = 6.0000000000000009e-001  area =   1.130400
radius = 8.0000000000000004e-001  area =   2.009600
radius = 1.0000000000000000e+000  area =   3.140000
radius = 1.2000000000000000e+000  area =   4.521600
radius = 1.3999999999999999e+000  area =   6.154400
radius = 1.5999999999999999e+000  area =   8.038400
radius = 1.7999999999999998e+000  area =  10.173600
radius = 1.9999999999999998e+000  area =  12.560000
radius = 2.1999999999999997e+000  area =  15.197600
radius = 2.3999999999999999e+000  area =  18.086400
radius = 2.6000000000000001e+000  area =  21.226400
radius = 2.8000000000000003e+000  area =  24.617600

 

#include <iostream>#include <iomanip>#include <string>using namespace std;int main( ) { ios_base::fmtflags flags = cout.flags( ); double pi = 3.14285714; cout << "pi = " << setprecision(5) << pi << '/n'; cout.flags(flags);}

 

pi = 3.1429

 

#include <iostream>#include <iomanip>#include <math.h>using namespace std;int main(){ double root2 = sqrt( 2.0 ); int places; cout << setiosflags( ios::fixed) << "Square root of 2 with precisions 0-9./n" << "Precision set by the " << "precision member function:" << endl; for ( places = 0; places <= 9; places++ ) { cout.precision( places ); cout << root2 << '/n'; } cout << "/nPrecision set by the " << "setprecision manipulator:/n"; for ( places = 0; places <= 9; places++ ) cout << setprecision( places ) << root2 << '/n'; return 0;}