Index
File
To use the fstream library in C++, you need to include both the standard <iostream> and the <fstream> header files. Here’s how you include them:
#include <iostream>
#include <fstream>
There are three classes included in the fstream library, which are used to create, write or read files:
| Class | Description |
|---|---|
ofstream | Creates and writes to files |
ifstream | Reads from files |
fstream | A combination of ofstream and ifstream: creates, reads, and writes to files |
Create and write to a file
To create a file in C++ using either the ofstream or fstream class and to write to the file using the insertion operator (<<), you can follow these steps:
- Include the necessary header file:
<fstream>for file stream operations. - Create an object of the
ofstreamorfstreamclass, specifying the name of the file you want to create. - Use the insertion operator (
<<) to write data to the file.
Example:
#include <iostream>
#include <fstream>
using namespace std;
int main() {
// Create and open a text file
ofstream MyFile("filename.txt");
// Write to the file
MyFile << "File is empty";
// Close the file
MyFile.close();
}
Read a file
To read from a file in C++ using either the ifstream or fstream class, and to read the file line by line using the getline() function within a while loop, you can follow these steps:
- Include the necessary header file:
<fstream>for file stream operations. - Create an object of the
ifstreamorfstreamclass, specifying the name of the file you want to read from. - Use the
getline()function within a while loop to read the file line by line. - Process the content of each line as needed.
Example:
#include <iostream>
#include <fstream> // For file stream operations
int main() {
// Create an object of ifstream or fstream class and specify the name of the file
std::ifstream inputFile("input.txt"); // This will open a file named "input.txt" for reading
// Check if the file is opened successfully
if (inputFile.is_open()) {
std::string line;
// Read the file line by line using getline() function
while (std::getline(inputFile, line)) {
// Process each line as needed
std::cout << line << std::endl; // Print the content of the line
}
// Close the file
inputFile.close();
} else {
// Display an error message if the file cannot be opened
std::cerr << "Unable to open file for reading." << std::endl;
return 1; // Return an error code
}
return 0; // Return 0 to indicate successful execution
}
Output:
Unable to open file for reading.
