C++ 流的使用 Part II - string stream 和 流的格式化输出

字符串流的使用。

继承图

示例代码：istringstream

#include <iostream>#include <string>#include <sstream>using namespace std;void main(){string strTest("12 45.67 ABCD");int i = 0;double d = 0;string str = "";istringstream s(strTest);s >> i >> d >> str ;    // the same as atof() and atoi(), atof() atoi() with higher performancecout << "int = " << i << endl;cout << "double = " << d << endl;cout << "string = " << str << endl;cin >> i;}

测试结果：

示例代码：ostringstream

#include <iostream>#include <string>#include <sstream>using namespace std;void main(){int i = 123;double d = 4.56;string str = "ABCDE";ostringstream os;os << "int =" << i << endl;os << "double =" << d << endl;os << "string =" << str << endl;string result = os.str();cout << "Result : " << endl << result << endl;cin >> i;}

输出流的格式化

开关标志

ios::unitbuf  ：  单元缓冲区每次插入后立即刷新（马上进行输出）。

ios::showpos  ：  在数字正数前加 "+"。


ios::skipws   ： 输入流中忽略空格。


ios::showpoint   ： 显示浮点值的小数点。

代码示例 输出格式化数字：

#include <iostream>#include <string>#include <sstream>using namespace std;void main(){int i = 123;double d = 4.56;string str = "ABCDE";ostringstream os;os << "int =" << i << endl;os << "double =" << d << endl;os << "string =" << str << endl;string result = os.str();cout << "Result : " << endl << result << endl;cin >> i;}

测试结果：






格式化域  ios::basefield

ios::hex : 输出 16 进制

ios::dec : 输出 10 进制

ios::oct : 输出 8 进制

ios::scientific : 输出科学计数法

ios::fixed : 以固定格式显示浮点数，与 setprecision(n) 连用。


ios::left  : 使输出左对齐。
ios::right : 使输出右对齐。


ios::width()   : 返回当前设置的宽度
ios::width(n)  : 设置当前的宽度


ios::fill()      : 返回当前设置填充字符
ios::fill(char)  : 设置当前的填充字符


ios::precision()   : 返回当前设置浮点数精度
ios::precision(n)  : 设置当前的浮点数精度

代码示例 输出控制：

#include <iostream>#include <string>#include <iomanip>using namespace std;void main(){    int i = 100;double d = 123.456;string str = "ABCD";cout << "i = " << i <<endl;cout << "d = " << d <<endl;cout << "i (hex) = " << hex << i << endl;cout << "i (dec) = " << dec << i << endl;cout << "i (oct) = " << oct << i << endl;cout << "d (scientific) = " << scientific << d << endl;cout << "d (fixed) = " << fixed << setprecision(6) << d << endl;  // total has 6 number after the pointcout.fill('#');cout.setf(ios::left);cout.width(10);cout<< i  << "   the fill chart is " << cout.fill() << endl;cout.fill('*');cout.setf(ios::right);cout.width(10);cout<<  i << "   the fill chart is " << cout.fill() << endl;cout.fill('-');cout.setf(ios::right);cout.width(10);cout<<  str << "   the fill chart is " << cout.fill() << endl;cin >> i;}

测试结果：