c++文件的读写

#include <iostream>
#include <fstream>
using namespace std;

int main(){
  int ar[] = {1123,123,43,45,63,43,2,3};
  //方法1，ios::out含义是也写的方式打开流
  ofstream ofile1("./test.txt", ios::out);
  //方法2
  ofstream ofile2;
  ofile2.open("./test.txt");                                                           
  if(!ofile1){//文件打开失败
    cerr << "open err" << endl;
    exit(1);
  }
  for(int i = 0; i < sizeof(ar) / sizeof(int); ++i){
    ofile1 << ar[i] << " ";
  }
  ofile1.close();
}

#include <iostream>
#include <fstream>
using namespace std;

int main(){
  int ar[10];
  ifstream ifile("./test.txt",ios::in);
  if(!ifile){
    cerr << "open err" << endl;
    exit(1);
  }
  for(int i = 0; i < 10; ++i){
    //用空格分割读进数组                                                          
    ifile >> ar[i];
  }
}

#include <iostream>
#include <fstream>
using namespace std;

int main(){
  int ar[] = {11,232,123123,1223,455,4,4,5,56,4,33};
  ofstream ofile("./text2.txt", ios::out | ios::binary);
  if(!ofile){
    cerr << "open err" << endl;
  }
  ofile.write((char*)ar, sizeof(ar));
  ofile.close();
}

#include <iostream>
#include <fstream>
using namespace std;

int main(){
  int ar[10];
  ifstream ifile("./text2.txt",ios::in | ios::binary);
  if(!ifile){
    cerr << "open err" << endl;
  }
  ifile.read((char*)ar, sizeof(ar));
  ifile.close();
}

#include <iostream>
#include <fstream>
using namespace std;

int main(){                                                                              
  ifstream ifile("./test.txt", ios::in);                                                 
  if(!ifile){                                                                            
    cerr << "open err" << endl;                                                          
  }                                                                                      
  int index;                                                                             
  int value;                                                                             
  while(1){                                                                              
    cin >> index;                                                                        
    ifile.seekg(index, ios::beg); //移动指针                                                      
    ifile >> value;                                                                      
    cout << value << endl;                                                               
  }                                                                                      
}  

#include <iostream>
#include <fstream>
using namespace std;
  
int main(){
  ifstream ifile("./test.txt", ios::in | ios::binary);
  if(!ifile){
    cerr << "open err" << endl;
  }
  int index;
  int value;
  while(1){
    cin >> index;
    ifile >> value;
    cout << value << endl;
  }
}