01. 输入输出流

        cout.setf(std::ios_base::dec);//设为十进制
	cout << 16 << endl;//打印十进制16

	cout.setf(std::ios_base::hex);//设为十六进制
	cout << 16 << endl;//打印10，没有0x前缀

	cout.setf(std::ios_base::oct);//设为八进制
	cout << 16 << endl;//打印20，没有0前缀
	
	cout.unsetf(std::ios_base::oct);//使指定标志位关闭
	cout << 16 << endl;//打印十进制16

	cout << std::hex << 16 << endl//std::hex内部调用setf
		<< std::oct << 16 << endl
		<< std::dec << 16 << endl;

	cout << std::showbase //std::showbase内部调用setf(ios_base::showbase)
		<< std::hex << 16 << endl//打印0x10
		<< std::oct << 16 << endl//打印020
		<< std::dec << 16 << endl;//打印16

	cout << std::hex << std::uppercase//浮点和十六进制整数的输出中使用大写
		<< 169 << endl//0XA9
		<< 179 << endl//0XB3
		<< 189 << endl//0XBD
		<< std::scientific
		<< 123.456 << endl//1.234560E+02
		<< 567.123 << endl;//1.234560E+02

        cout.setf(std::ios_base::scientific, std::ios_base::floatfield);//设置flag
	cout << 2345.678 << endl;//2.345678e+03

	cout.unsetf(std::ios_base::scientific);//取消flag
	cout << 2345.678 << endl;//2345.68

	cout << std::scientific //std::scientific内部调用setf
		<< 2345.678 << endl;//2.345678e+03

	cout.setf(std::ios_base::fixed, std::ios_base::floatfield);//设置flag
	cout << 2345.678 << endl;//2345.68

	cout << std::fixed << 2345.678 << endl;//std::fixed内部调用setf

        cout.precision(6);//设置精度为3
	cout << 2345.678 << endl;//2345.68

        cout.width(10);
	cout.fill(‘$‘);//设置填充字符，默认为空格
	cout << std::right << "Hello" << endl;//打印$$$$$Hello

	cout.width(10);//再调用一次
	cout << std::left << "Hello" << endl;//Hello$$$$$