C语言里可以用printf(),%f来实现浮点数的格式化输出，用cout呢。。。？
下面的方法是在网上找到的，如果各位有别的办法谢谢留下... iomanip.h是I/O流控制头文件,就像C里面的格式化输出一样.以下是一些常的: dec 置基数为10 相当于"%d"
hex 置基数为16 相当于"%X"
oct 置基数为8 相当于"%o"
setfill(c) 设填充字符为c
setprecision(n) 设显示小数精度为n位
setw(n) 设域宽为n个字符
setioflags(ios::fixed) 固定的浮点显示
setioflags(ios::scientific) 指数表示
setiosflags(ios::left) 左对齐
setiosflags(ios::right) 右对齐
setiosflags(ios::skipws 忽略前导空白
setiosflags(ios::uppercase) 16进制数大写输出
setiosflags(ios::lowercase) 16进制小写输出
setiosflags(ios::showpoint) 强制显示小数点
setiosflags(ios::showpos) 强制显示符号 #include <iomanip>
use namespace std; double d=11.23456;
cout<<d<<endl; //直接输出只能输出6位数，包括整数部分和小数部分
cout<<setprecision()<<d<<endl; //精度为3，输出3位数
cout<<setiosflags(ios::fixed)<<d<<endl;//精度为3，定点输出，输出3位小数
cout<<setiosflags(ios::fixed)<<setprecision()<<d<<endl;//位数不够，末尾添0 输出结果：
11.2346
11.2
11.23456
11.2345600 C++格式化输出浮点数 view plaincopy to clipboardprint?
.#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 ;
.}
#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 ;
} 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 view plaincopy to clipboardprint?
.#include <iostream.h>
.
.main(void)
.{
. float a=100100.0, b=0.08;
. cout.setf(ios::right|ios::scientific|ios::showpoint);
. cout.width();
. cout <<(-a*b);
.
. return ;
.}
#include <iostream.h> main(void)
{
float a=100100.0, b=0.08;
cout.setf(ios::right|ios::scientific|ios::showpoint);
cout.width();
cout <<(-a*b);
return ;
} -8.008000e+003 view plaincopy to clipboardprint?
.#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 = . ; radius <= 3.0 ; radius += .)
. cout << "radius = "
. << setprecision(numeric_limits<double>::digits10 + )
. << std::scientific << radius<< " area = "
. << std::setw() << setprecision()<< std::fixed << pi * radius * radi
.us << endl;
. return ;
.}
#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 = . ; radius <= 3.0 ; radius += .)
cout << "radius = "
<< setprecision(numeric_limits<double>::digits10 + )
<< std::scientific << radius<< " area = "
<< std::setw() << setprecision()<< std::fixed << pi * radius * radi
us << endl;
return ;
} 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 view plaincopy to clipboardprint?
.#include <iostream>
.#include <iomanip>
.#include <string>
.
.using namespace std;
.
.int main( ) {
.
. ios_base::fmtflags flags = cout.flags( );
.
. double pi = 3.14285714;
.
. cout << "pi = " << setprecision() << pi << '\n';
.
. cout.flags(flags);
.}
#include <iostream>
#include <iomanip>
#include <string> using namespace std; int main( ) { ios_base::fmtflags flags = cout.flags( ); double pi = 3.14285714; cout << "pi = " << setprecision() << pi << '\n'; cout.flags(flags);
} pi = 3.1429 view plaincopy to clipboardprint?
.#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 = ; places <= ; places++ ) {
. cout.precision( places );
. cout << root2 << '\n';
. }
.
. cout << "\nPrecision set by the "
. << "setprecision manipulator:\n";
.
. for ( places = ; places <= ; places++ )
. cout << setprecision( places ) << root2 << '\n';
.
. return ;
.}