C++ Tutorial/File Stream/file open mode

Appending to the End of a File

<source lang="cpp">#include <fstream>

1. include <iostream>

using namespace std; int main() {

  char buffer[255];
  ifstream fin("text.txt");
  if (fin)              
  {
     char ch;
     while (fin.get(ch))
        cout << ch;
  }
  fin.close();
  cout << "in append mode...\n";
  ofstream fout("text.txt",ios::app);
  if (!fout)
  {
     cout << "Unable to open for appending.\n";
     return(1);
  }
  cout << "\nEnter text for the file: ";
  cin.ignore(1,"\n");
  cin.getline(buffer,255);
  fout << buffer << "\n";
  fout.close();
  fin.open("text.txt");  
  if (!fin)
  {
     cout << "Unable to open for reading.\n";
     return(1);
  }
  char ch;
  while (fin.get(ch))
     cout << ch;
  fin.close();
  return 0;

}</source>

Open a file as binary file and get its size

<source lang="cpp">#include <fstream>

1. include <iostream>

using namespace std; int main () {

 long start,end;
 ifstream myfile ("test.txt", ios::in|ios::binary);
 
 start = myfile.tellg();
 myfile.seekg (0, ios::end);
 end = myfile.tellg();
 myfile.close();
 
 cout << "size of " << "test.txt";
 cout << " is " << (end-start) << " bytes.\n";
 return 0;

}</source>

size of test.txt is 25 bytes.

Open a file for appending and append

<source lang="cpp">#include <fstream>

1. include <iostream>

using namespace std;

int main () {

 char buffer[256];

 fstream myfile;
 //open for appending and append
 myfile.open("test.txt",ios::app);
 myfile << " Hey this is another line \n";
 myfile.close();

 return 0;

}</source>

Open a file for input and read in its content

<source lang="cpp">#include <fstream>

1. include <iostream>

using namespace std;

int main () {

 char buffer[256];

 fstream myfile;
 // open it for input and read in
 myfile.open("test.txt",ios::in);
 myfile.getline(buffer,100);
 cout << "The file contains   " << buffer << "\n";
 myfile.close();

 return 0;

}</source>

The file contains   This outputting a line.

Opening files for read and write.

<source lang="cpp">#include <fstream>

1. include <iostream>

using namespace std; int main() {

  char buffer[255];    
  ofstream fout("text.txt");
  fout << "test\n";
  cout << "Enter text for the file: ";
  cin.ignore(1,"\n"); 
  cin.getline(buffer,255);
  fout << buffer << "\n"; 
  fout.close();           
  ifstream fin("text.txt"); 
  char ch;
  while (fin.get(ch))
     cout << ch;
  fin.close();
return 0;

}</source>

Opening text Files for Read and Write

<source lang="cpp">#include <fstream>

1. include <iostream>

using namespace std; int main() {

  char buffer[255];
  ofstream fout("text.txt");
  fout << "this is a test\n";
  cout << "Enter text for the file: ";
  cin.ignore(1,"\n");  
  cin.getline(buffer,255);  
  fout << buffer << "\n";   
  fout.close();             
  ifstream fin("text.txt");
  cout << "Here"s the contents of the file:\n";
  char ch;
  while (fin.get(ch))
     cout << ch;
  fin.close();            
  return 0;

}</source>