cout.setf() 与 cout.precision()

大家都知道 ：cout.setf()是用来设置位的，cout.precision()是用来设置精度的，但具体如何操作想必难倒一批人！

std::ios_base::setf   或者 std::ios::setf

 

C++

 

Input/output library

 

std::ios_base

 

fmtflags setf( fmtflags flags );	(1)
fmtflags setf( fmtflags flags, fmtflags mask );	(2)

Sets the formatting flags to specified settings.

1) Sets the formatting flags to flags

2) Clears the formatting flags under mask, and sets the cleared flags to those specified by flags. Essentially the following operation is performed  (flags & mask) where fl defines the state of internal formatting flags.

Parameters

flags, mask

-

new formatting setting. mask defines which flags can be altered, flags defines which flags of those to be altered should be set (others will be cleared). Both parameters can be a combination of the following constants: Constant Explanation   dec use decimal base for integer I/O   oct use octal base for integer I/O   hex use hexadecimal base for integer I/O   basefield dec|oct|hex|0. Useful for masking operations    由此向上四个是一组   left left adjustment (adds fill characters to the right)   right right adjustment (adds fill characters to the left)   internal internal adjustment (adds fill characters to the internal designated point)   adjustfield left|right|internal. Useful for masking operations   由此向上四个是一组   scientific generate floating point types using scientific notation, or hex notation if combined with fixed   fixed generate floating point types using fixed notation, or hex notation if combined with scientific   floatfield scientific|fixed|(scientific|fixed)|0. Useful for masking operations   由此向上3个是一组   boolalpha insert and extract bool type in alphanumeric format   showbase generate a prefix indicating the numeric base for integer output, require the currency indicator in monetary I/O   showpoint generate a decimal-point character unconditionally for floating-point number output   showpos generate a + character for non-negative numeric output   skipws skip leading whitespace before certain input operations   unitbuf flush the output after each output operation   uppercase replace certain lowercase letters with their uppercase equivalents in certain output output operations

例子：

#include
using  namespace  std;

int  main () {
  cout.setf ( ios::hex, ios::basefield );        // set hex as the basefield
  cout.setf ( ios::showbase );                   // activate showbase
  cout << 100 << endl;
  cout.setf ( 0, ios::showbase );                // deactivate showbase
  cout << 100 << endl;
  return  0;
}

输出：
0x64
64

setprecision：

#include
#include
using  namespace  std;

int  main () {
  double  f =3.14159;
  cout << setprecision (5) << f << endl;
  cout << setprecision (9) << f << endl;
  cout << fixed;
  cout << setprecision (5) << f << endl;
  cout << setprecision (9) << f << endl;
  return  0;
}

输出：
3.1416
3.14159
3.14159
3.141590000

参考网址：

http://en.cppreference.com/w/cpp/io/ios_base/setf