opening file in c++

// reading a text file
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main () {
  string line;
  ifstream myfile ("example.txt");
  if (myfile.is_open())
  {
    while ( getline (myfile,line) )
    {
      //use line here
    }
    myfile.close();
  }

  else cout << "Unable to open file"; 

  return 0;
}

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

ifstream file_variable; //ifstream is for input from plain text files
file_variable.open("input.txt"); //open input.txt

file_variable.close(); //close the file stream
/*
Manually closing a stream is only necessary
if you want to re-use the same stream variable for a different
file, or want to switch from input to output on the same file.
*/
_____________________________________________________
//You can also use cin if you have tables like so:
while (cin >> name >> value)// you can also use the file stream instead of this
{
 cout << name << value << endl;
}
_____________________________________________________
//ifstream file_variable; //ifstream is for input from plain text files
ofstream out_file;
out_file.open("output.txt");

out_file << "Write this scentence in the file" << endl;

/ fstream::open / fstream::close
#include <fstream>      // std::fstream

int main () {

  std::fstream fs;
  fs.open ("test.txt", std::fstream::in | std::fstream::out | std::fstream::app);

  fs << " more lorem ipsum";

  fs.close();

  return 0;
}

// basic file operations
#include <iostream>
#include <fstream>
using namespace std;

int main () {
  ofstream myfile;
  myfile.open ("example.txt");
  myfile << "Writing this to a file.\n";
  myfile.close();
  return 0;
}

/* File Handling with C++ using fstream class object */
/* To write the Content in File */
/* Then to read the content of file*/
//nice
#include <iostream> 
  
/* fstream header file for ifstream, ofstream,  
   fstream classes */
#include <fstream> 
  
using namespace std; 
  
// Driver Code 
int main() 
{ 
    // Creation of fstream class object 
    fstream fio; 
  
    string line; 
  
    // by default openmode = ios::in|ios::out mode 
    // Automatically overwrites the content of file, To append 
    // the content, open in ios:app 
    // fio.open("sample.txt", ios::in|ios::out|ios::app) 
    // ios::trunc mode delete all conetent before open 
    fio.open("sample.txt", ios::trunc | ios::out | ios::in); 
  
    // Execute a loop If file successfully Opened 
    while (fio) { 
  
        // Read a Line from standard input 
        getline(cin, line); 
  
        // Press -1 to exit 
        if (line == "-1") 
            break; 
  
        // Write line in file 
        fio << line << endl; 
    } 
  
    // Execute a loop untill EOF (End of File) 
    // point read pointer at beginning of file 
    fio.seekg(0, ios::beg); 
  
    while (fio) { 
  
        // Read a Line from File 
        getline(fio, line); 
  
        // Print line in Console 
        cout << line << endl; 
    } 
  
    // Close the file 
    fio.close(); 
  
    return 0; 
}