open a file c++ code example

Example 1: read a file 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;
}

Example 2: c++ files

// 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;
}

Example 3: opening file in c++

/ 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;
}

Example 4: How to read a file in in C++

// io/read-file-sum.cpp - Read integers from file and print sum.
// Fred Swartz 2003-08-20

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

int main() {
    int sum = 0;
    int x;
    ifstream inFile;
    
    inFile.open("test.txt");
    if (!inFile) {
        cout << "Unable to open file";
        exit(1); // terminate with error
    }
    
    while (inFile >> x) {
        sum = sum + x;
    }
    
    inFile.close();
    cout << "Sum = " << sum << endl; 
    return 0;
}