c++ ios_base类

 ios_base is  Base class with type-independent members for the standard stream classes(ios);

其中有一个成员函数

ios_base::flags 用来控制流的格式。

fmtflags flags ( ) const;  
fmtflags flags ( fmtflags fmtfl );

Get/set format flags

The first syntax returns the current set of format flags set for the stream.
The second syntax sets a new set of format flags for the stream, returning its former value.

其中的参数类型为public member type ，ios_base::fmtflags 是Type for stream format flags；

 有很多字段 ，

如  showbase，展示是几进制

 uppercase

numerical base (basefield)	dec	read/write integral values using decimal base format.
	hex	read/write integral values using hexadecimal base format.
	oct	read/write integral values using octal base format.
float format  (floatfield)	fixed	write floating point values in fixed-point notation.
	scientific	write floating-point values in scientific notation.

参考http://www.cplusplus.com/reference/iostream/ios_base/fmtflags/，

示例程序：

// modify flags
#include <iostream>
using namespace std;

int main () {
  cout.flags ( ios::right | ios::hex | ios::showbase );
  cout.width (10);
  cout << 100;
  return 0;
}

0x64

This simple example sets some format flags for cout that affect the latter insertion operation by printing the value in hexadecimal base format (0x64) padded right as in a field ten spaces long:影响后来的流插入符。

还可以这么写，用操作符来进行控制：

#include <iostream>
#include <iomanip>
using namespace std;

int main () {
  cout << hex << setiosflags (ios_base::showbase | ios_base::uppercase);
  cout << 100 << endl;
  return 0;
}

0x64

这里setiosflags是个manipulator。

setiosflags(ios::XXX)可以直接写成XXX。 如：cout<<setiosflags(ios::flxed)   cout<<fixed