File Handling

In C++, files are mainly dealt by using three classes fstream, ifstream, ofstream available in fstream headerfile.
ofstream: Stream class to write on files
ifstream: Stream class to read from files
fstream: Stream class to both read and write from/to files.

Now the first step to open the particular file for read or write operation. We can open file by
1. passing file name in constructor at the time of object creation
2. using the open method
For e.g.

Open File by using constructor
ifstream (const char* filename, ios_base::openmode mode = ios_base::in);
ifstream fin(filename, openmode) by default openmode = ios::in
ifstream fin(“filename”);

Open File by using open method
Calling of default constructor
ifstream fin;

fin.open(filename, openmode)
fin.open(“filename”);

Modes :

MEMBER CONSTANT	STANDS FOR	ACCESS
in *	input	File open for reading: the internal stream buffer supports input operations.
out	output	File open for writing: the internal stream buffer supports output operations.
binary	binary	Operations are performed in binary mode rather than text.
ate	at end	The output position starts at the end of the file.
app	append	All output operations happen at the end of the file, appending to its existing contents.
trunc	truncate	Any contents that existed in the file before it is open are discarded.

Default Open Modes :

ifstream	ios::in
ofstream	ios::out
fstream	ios::in | ios::out

Below is the implementation by using fstream class.:

/* File Handling with C++ using ifstream & ofstream class object*/
/* To write the Content in File*/
/* Then to read the content of file*
#include <iostream>
/* fstream header file for ifstream, ofstream,  
fstream classes */
#include <fstream> 
using namespace std;

// Creation of ofstream class object
int main()
string line; 
ofstream fout;
// by default ios::out mode, automatically deletes 
// the content of file. To append the content, open in ios:app 
// fout.open("sample.txt", ios::app) 
fout.open("sample.txt"); 

// Execute a loop If file successfully opened 
while (fout) { 

    // Read a Line from standard input 
    getline(cin, line); 

    // Press -1 to exit 
    if (line == "-1") 
        break; 

    // Write line in file 
    fout << line << endl; 
} 

// Close the File 
fout.close(); 

// Creation of ifstream class object to read the file 
ifstream fin; 

// by default open mode = ios::in mode 
fin.open("sample.txt"); 

// Execute a loop until EOF (End of File) 
while (fin) { 

    // Read a Line from File 
    getline(fin, line); 

    // Print line in Console 
    cout << line << endl; 
} 

// Close the file 
fin.close(); 

return 0;