C++ File Handling

C++ has a standard library fstream which is used for file handling. <fstream> header file must be included in your program to process files. It has three data types ofstream, ifstream and fstream.

ofstream

ofstream is the output file stream which is used to create files and to write information to files.

ifstream

ifstream is the input file stream which is used to read information from files.

fstream

fstream is the general file stream which can be used to create files, write information to files, and read information from files.

Opening a file

If you want to write or read from a file first you must open the file. ifstream object is used to open a file to just read from it, ofstream and fstream objects can be used to open a file for writing. The open() function is a member of fstream, ifstream, and ofstream objects. The first argument specifies the name and location of the file and second argument specifies the mode in which the file should be opened.

fstream myFile;
myFile.open(“myFile.txt”, ios::out | ios::in );

Mode Description
ios::app The output to that file will be appended to the end.
ios::ate Move the read/write control to the end of the file.
ios::in Open the file for reading.
ios::out Open the file for writing.
ios::trunc The contents will be truncated before opening the file if it already exists.

Closing a file

The close() function is is a member of fstream, ifstream, and ofstream objects and used to close opened files. C++ automatically flush all the streams, opened files and release allocated memory when a program terminates. But it is good practice to close all the opened files before program termination. Following is the syntax to close a file.

void close();

Writing & reading from a file

The stream insertion operator (<<) is used with the ofstream or fstream object to write information to a file. The stream extraction operator (>>) is used with the ifstream or fstream object to read information from a file.

File Handling Example

#include <fstream>
#include <iostream>

using namespace std;

int main () {

char data[50];

ofstream myFile;
myFile.open(“myFile.txt”);

cin.getline(data, 50);

//writing information into the file
myFile << data << endl;

//closing file
myFile.close();

//opening the file in read mode
ifstream oldFile;
oldFile.open(“myFile.txt”);

oldFile >> data;

//printing the data on screen.
cout << data << endl;

//closing file
oldFile.close();

return 0;

}

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