Understanding and Using the PHP fseek() Function

The fseek() function moves the file pointer to a specified location, enabling various file operations such as reading, writing, or appending data.

Syntax of fseek()

<code>fseek(file, offset, whence)</code>

file : required; the file resource opened by fopen() .

offset : required; the number of bytes to move the pointer (positive, negative, or zero).

whence : optional; determines how the offset is interpreted. Possible values are:

SEEK_SET (default): set pointer to the beginning of the file.

SEEK_CUR : set pointer relative to the current position.

SEEK_END : set pointer relative to the end of the file.

Example usage of fseek()

<code><?php
$file = fopen("example.txt", "r+");
if ($file) {
    // Move pointer to the beginning
    fseek($file, 0, SEEK_SET);

    // Read first 10 bytes
    echo fread($file, 10);

    // Move pointer to the end
    fseek($file, 0, SEEK_END);

    // Write new line
    fwrite($file, "This is a new line.");

    // Move pointer back to the beginning
    fseek($file, 0, SEEK_SET);

    // Read entire file
    echo fread($file, filesize("example.txt"));

    // Close file
    fclose($file);
}
?>
</code>

The example opens a file in read‑write mode, uses fseek() to position the pointer at the start, reads bytes, moves to the end, writes new data, returns to the start, reads the whole file, and finally closes it.

Overall, fseek() is a flexible and essential PHP function for precise file positioning, allowing developers to add, delete, or modify data efficiently.