C++ IO库：cmd读写，字符串读写，文件读写，＜＜重载，标准输出

1、三个头文件

iostream: istream+ostream

//读写流 #include<iostream> using namespace std; int main(){ int a, b; cin>>a>>b; cout<<a+b<<endl; return 0; }

fstream:ifstream+ofstream

//读写文件 #include<fstream> using namespace std; int main(){ int a, b, c; ifstream in1; in1.open("input.txt"); ofstream out1; out1.open("output.txt", ofstream::app); in1>>a>>b; out1<<a+b<<endl; return 0; }

sstream=istringstream+ostringstream

//读写字符串 #include<iostream> #include<sstream> using namespace std; int main(){ string a = "abcde"; istringstream st1; //定义输入流 st1.str(a); //拷贝内容到流中 string b = st1.str();//返回流中内容 string c; st1>>c;//输出内容到流中 ostringstream st2; //定义输出流 st2<<a<<"12345"; //输出内容到流中 string d = st2.str(); //返回流中内容 cout<<b<<" "<<c<<" "<<d<<endl; return 0; }

2、输出格式

#include<iostream> #include<iomanip>//不要忘记包含此头文件 using namespace std; int main(){ int a; cout<<"input a:"; cin>>a; cout<<"dec:"<<dec<<a<<endl; //以十进制形式输出整数 cout<<"hex:"<<hex<<a<<endl; //以十六进制形式输出整数a cout<<"oct:"<<setbase(8)<<a<<endl; //以八进制形式输出整数a char *pt="China"; //pt指向字符串"China" cout<<setw(10)<<pt<<endl; //指定域宽为,输出字符串 cout<<setfill('*')<<setw(10)<<pt<<endl; //指定域宽,输出字符串,空白处以'*'填充 double pi=22.0/7.0; //计算pi值 //按指数形式输出,8位小数 cout<<setiosflags(ios::scientific)<<setprecision(8); cout<<"pi="<<pi<<endl; //输出pi值 cout<<"pi="<<setprecision(4)<<pi<<endl; //改为位小数 cout<<"pi="<<setiosflags(ios::fixed)<<pi<<endl; //改为小数形式输出 return 0; }

3、<<重载

>>运算符左侧为流输入对象，右侧为结构对象，返回一个流输入对象。 注意引用符号&

istream& operator>>(istream& in, complex& A){ in >> A.m_real >> A.m_imag; return in; }

实现pair，complex类型。

#include <iostream> using namespace std; class complex{ public: complex(double real = 0.0, double imag = 0.0): m_real(real), m_imag(imag){ }; public: friend complex operator+(const complex & A, const complex & B); friend complex operator-(const complex & A, const complex & B); friend complex operator*(const complex & A, const complex & B); friend complex operator/(const complex & A, const complex & B); friend istream & operator>>(istream & in, complex & A); friend ostream & operator<<(ostream & out, complex & A); private: double m_real; //实部 double m_imag; //虚部 }; //重载加法运算符 complex operator+(const complex & A, const complex &B){ complex C; C.m_real = A.m_real + B.m_real; C.m_imag = A.m_imag + B.m_imag; return C; } //重载减法运算符 complex operator-(const complex & A, const complex &B){ complex C; C.m_real = A.m_real - B.m_real; C.m_imag = A.m_imag - B.m_imag; return C; } //重载乘法运算符 complex operator*(const complex & A, const complex &B){ complex C; C.m_real = A.m_real * B.m_real - A.m_imag * B.m_imag; C.m_imag = A.m_imag * B.m_real + A.m_real * B.m_imag; return C; } //重载除法运算符 complex operator/(const complex & A, const complex & B){ complex C; double square = A.m_real * A.m_real + A.m_imag * A.m_imag; C.m_real = (A.m_real * B.m_real + A.m_imag * B.m_imag)/square; C.m_imag = (A.m_imag * B.m_real - A.m_real * B.m_imag)/square; return C; } //重载输入运算符 istream& operator>>(istream& in, complex& A){ in >> A.m_real >> A.m_imag; return in; } //重载输出运算符 ostream& operator<<(ostream& out, complex& A){ out << A.m_real <<" + "<< A.m_imag <<" i ";; return out; } int main(){ complex c1, c2, c3; cin>>c1>>c2; c3 = c1 + c2; cout<<"c1 + c2 = "<<c3<<endl; c3 = c1 - c2; cout<<"c1 - c2 = "<<c3<<endl; c3 = c1 * c2; cout<<"c1 * c2 = "<<c3<<endl; c3 = c1 / c2; cout<<"c1 / c2 = "<<c3<<endl; return 0; }