The fwrite() function in PHP is used to write data (string or binary) to an open file. Before using fwrite(), you need to open the file with fopen(). Once the file is open, fwrite() sends your data to that file.
Syntax:
fwrite(resource $handle, string $string, int $length = null): int|false
In this syntax:
The fwrite() function in PHP accepts three parameters.
- $handle: The file resource obtained from fopen() or similar functions.
- $string: The string data you want to write to the file.
- $length (optional): The maximum number of bytes that you want to write.
Return Value:
It returns the number of bytes written on success, or False on failure.
Note: The fwrite() function was initially introduced in core PHP 4 and continues to be fully supported in PHP 5, PHP 7, and PHP 8.
How Does fwrite() Work?
The general process of writing to a file using fwrite() involves these steps:
- Open the file using fopen() with an appropriate mode (e.g., w for write, a for append).
- Use fwrite() to write your string data to the file.
- Close the file with fclose() to free resources and save changes.
Writing to a New File
We open the file example.txt in write mode ("w"). Then, we write a string of text into the file using fwrite(). After writing, we close the file with fclose() to save the changes.
PHP <?php $file = "example.txt"; // Open file for writing $handle = fopen($file, "w"); if ($handle) { $text = "Hello, this is a sample text.\nWelcome to fwrite() function."; $bytesWritten = fwrite($handle, $text); echo "Wrote $bytesWritten bytes to $file"; fclose($handle); } else { echo "Failed to open the file."; } ?> Output:
PHP fwrite( ) FunctionAppending Data to an Existing File
We open the file example.txt in append mode ("a"), which lets us add data without deleting what’s already there. Then, we write a new line at the end of the file using fwrite(). Finally, we close the file with fclose().
PHP <?php $file = "example.txt"; $handle = fopen($file, "a"); if ($handle) { $newLine = "\nAdding a new line to the file."; fwrite($handle, $newLine); fclose($handle); echo "Data appended successfully."; } else { echo "Unable to open the file."; } ?> Output:
Writing Binary Data to a File
In this example, we open a file named data.bin in binary write mode. We then create some binary content using PHP’s pack() function to convert numbers into binary format. This binary data is written to the file, and finally, the file is closed.
PHP <?php // Open the file in binary write mode $fileHandle = fopen("data.bin", "wb"); // Create binary data representing some unsigned short integers $binaryContent = pack("S*", 1234, 5678, 910, 1122); // Write the binary data into the file fwrite($fileHandle, $binaryContent); // Close the file to save changes fclose($fileHandle); echo "Binary data successfully saved."; ?> Output:
PHP fwrite( ) FunctionBest Practices for Using the fwrite() Function
- Always check if the file opens successfully before writing.
- Use the correct file mode (w, a, wb, etc.) based on your needs.
- Close the file after writing with fclose() to save changes.
- Use file locking (flock()) when multiple processes may write simultaneously.
- Validate and sanitize data before writing to avoid security issues.
Conclusion
The PHP fwrite() function is essential for writing data to files. It works together with fopen() to open files and fclose() to close them. Whether you want to create new files, update existing ones, or write partial data, fwrite() provides an efficient way to do so.With proper error handling and the right file modes, you can safely and effectively manage file writing operations in your PHP applications.