C++ ofstream Class

❮ fstream classes

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

int main() {
  // Create and open a text file
  ofstream MyFile("filename.txt");

  // Write to the file
  MyFile << "Files can be tricky, but it is fun enough!";

  // Close the file
  MyFile.close();
} 

Definition and Usage

The ofstream class (short for "output file stream") is used to write into files.

The ofstream class is defined in the <fstream> header file.

To open a file, pass the file path into the constructor:

ofstream MyFile("filename.txt");

The << insertion operator and a variety of functions can be used to write into the file.

The Insertion Operator

The << insertion operator writes a literal value or the contents of a variable into the file.

int year = 2024;
MyFile << year << "\n";
MyFile << "Files can be tricky, but it is fun enough!";

Manipulators

Manipulators change the formatting of the data that is written to the file. They are used with the << insertion operator in the same way as literal values and variables.

Except for setw(), the effect of a manipulator remains until another another manipulator changes it.

Some useful manipulators are shown in the table below.

File Writing Functions

The file writing functions write data into a file and move the file pointer to the first position after the written content.

write()

The write(str, n) method writes n characters from the char array str into the file.

char myStr[] = "Hello World!";
MyFile.write(myStr, 5);

put()

The put(c) method writes the specified character c into the file.

char grade = 'B';
MyFile.put(grade);

File Handling Functions

File handling functions open, close and navigate files.

open()

The open(filepath) method opens the file at the path specified by filepath. If a file is already open then this method has no effect.

ofstream MyFile;
MyFile.open("filename.txt");

is_open()

The is_open() method returns true if a file is open and false if there is no file open.

ofstream MyFile;
cout << MyFile.is_open(); << "\n"; // Displays 0 because the file is not open
MyFile.open("filename.txt");
cout << MyFile.is_open(); << "\n"; // Displays 1 because the file is open

close()

The close() method closes a file. It is good to close a file when you are finished working with it to free up resources.

MyFile.close();

rdbuf()

The rdbuf() method returns a pointer to the internal filebuf object which directly handles the file.

filebuf * buf = MyFile.rdbuf();

seekp()

The seekp(position) method moves the file pointer to a specified position relative to the beginning of the file.

MyFile.seekp(6)

The seekp(position, origin) method moves the file pointer to a specified position in the file relative to an origin. The origin has three possible values:

• ofstream::beg - The position is relative to the beginning of the file.
• ofstream::cur - The position is relative to the current file position.
• ofstream::end - The position is relative to the end of the file.

MyFile.seekp(6, ofstream::beg);
cout << MyFile.tellp(); << "\n";
MyFile.seekp(-3, ofstream::cur);
cout << MyFile.tellp(); << "\n";
MyFile.seekp(-4, ofstream::end);
cout << MyFile.tellp(); << "\n";

tellp()

The tellp() method returns the current position of the file pointer in the file.

cout << MyFile.tellp();

❮ fstream classes