C++ IO库：cmd读写，字符串读写，文件读写，＜＜重载，标准输出

原创

小哈里1139 2023-02-08 15:14:59 博主文章分类：ICPC ©著作权

文章标签 ios 运算符 #include 文章分类 Python 后端开发

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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;
}