每一个 iostream 库对象都维护一个格式状态(format state),它控制格式化操作的细节,比如整型值的进制数或浮点数值的精度。C++为程序员提供了一组预定义的操作符(manipulator),可用来修改对象的格式状态。操作符不会导致读写数据,只是改变流对象的内部状态。
1. boolalpha/noboolalpha操作符
bool flag = true;
cout << flag << endl;
cout << boolalpha;
cout << flag << endl;
cout << noboolalpha;
cout << flag << endl;
输出结果:
2. hex、oct、dec操作符
int iVal = 0x11;
cout << "Octal: " << oct << iVal << endl;
cout << "Decimal: " << dec << iVal << endl;
cout << "Hexadecimal: " << hex << iVal << endl;
输出结果:
3. showbase/noshowbase操作符
int iVal = 0x11;
cout << showbase;
cout << "Octal: " << oct << iVal << endl;
cout << "Decimal: " << dec << iVal << endl;
cout << "Hexadecimal: " << hex << iVal << endl;
cout << noshowbase;
输出结果:
4. uppercase/nouppercase
int iVal = 0x11;
cout << showbase << uppercase;
cout << "Octal: " << oct << iVal << endl;
cout << "Decimal: " << dec << iVal << endl;
cout << "Hexadecimal: " << hex << iVal << endl;
cout << noshowbase << nouppercase;
输出结果:
5. precision()/precision(n)成员函数
double dVal = 3.1415926;
int Accuracy = cout.precision();
cout << Accuracy << endl;
cout << dVal << endl;
cout.precision(3);
cout << dVal << endl;
输出结果:
6. setprecision(n)操作符(#include <iomanip>)
double dVal = 3.1415926;
cout << dVal << endl;
cout << setprecision(3);
cout << dVal << endl;
输出结果:
7. showpoint操作符
cout << 10.00 << endl;
cout << showpoint;
cout << 10.00 << endl;
输出结果:
8. scientific/fixed操作符
cout << scientific;
cout << 10.0 << endl;
cout << fixed;
cout << 10.0 << endl;
输出结果:
如果希望把'e'输出为'E',则可以使用uppercase操作符,使用nouppercase操作符再次转换成小写。
9. noskipws/skipws
infile所关联的文本文件的内容为:
a b c
d
代码1:
while (infile >> ch)
{
cout.put(ch);
}
输出结果:
代码2:
infile >> noskipws;
while (infile >> ch)
{
cout.put(ch);
}
infile >> skipws;
输出结果:
10. setw()操作符
int iVal = 16;
double dVal = 3.14159;
cout << setw(6) << iVal << endl;
cout << setw(12) << dVal << endl;
输出结果:
11. setfill()操作符
int iVal = 16;
double dVal = 3.14159;
cout << setw(10) << setfill('%');
cout << iVal << endl;
cout << setw(10) << setfill('%');
cout << dVal << endl;
输出结果:
12. left/right操作符
代码1:
int iVal = 16;
double dVal = 3.14159;
cout << left;
cout << setw(10) << setfill('%');
cout << iVal << endl;
cout << setw(10) << setfill('%');
cout << dVal << endl;
cout << right;
输出结果:
代码2:
int iVal = 16;
double dVal = 3.14159;
cout << right;
cout << setw(10) << setfill('%');
cout << iVal << endl;
cout << setw(10) << setfill('%');
cout << dVal << endl;
cout << left;
输出结果:
DNFM0047(0)