What is fwrite() in PHP?

fwrite() is a built-in PHP function used to write data to a file.

• It writes content to an open file (opened using functions like fopen()).
• If the file doesn't exist and you opened it in a mode like 'w' or 'w+', it creates a new file.
• You can specify how much to write by providing an optional third parameter (length).

Basic Syntax

fwrite(resource $stream, string $string, int $length = ?): int|false

• $stream — the file handle (opened using fopen()).
• $string — the content you want to write.
• $length (optional) — how many bytes you want to write.

It returns the number of bytes written, or false on failure.

Simple Example: Write to a File

<?php
$file = fopen("example.txt", "w"); // Open for writing, creates if not exists

if ($file) {
    fwrite($file, "Hello, World!");
    fclose($file); // Always close your file
    echo "Data written successfully.";
} else {
    echo "Unable to open the file.";
}
?>

🔹 This code will create (or overwrite) example.txt and write "Hello, World!" inside it.

Example with Specifying Length

<?php
$file = fopen("example2.txt", "w");

if ($file) {
    $text = "Welcome to PHP fwrite function!";
    fwrite($file, $text, 7); // Only writes "Welcome"
    fclose($file);
}
?>

🔹 Here, only the first 7 characters ("Welcome") will be written into the file.

Appending Data Instead of Overwriting

<?php
$file = fopen("example.txt", "a"); // 'a' mode means append

if ($file) {
    fwrite($file, "\nThis is a new line!");
    fclose($file);
}
?>

🔹 Using 'a' mode, the new content is added at the end without removing existing content.

Important Points

• Always check if the file opened successfully before calling fwrite().
• Always close the file after writing with fclose().
• If you use "w" mode, it erases the existing content.
• Use "a" mode to append without deleting the old content.