About a file pointer in PHP

Question

I am just now training PHP. About the following code,I read a schedule from file,and overwrite or delete if there is given line number($lineNo) in file.

Then I have a question. Is when a file pointer is updated when fwrite function have carried out?

<?php
    $filename = "sample.txt";
    function edit($filename,$lineNo){
        $new_line = "Hello";
        $schedule_list = file($filename);
        $fp = fopen($filename,"w");
        foreach($schedule_list as $schedule_lineNo => $line){
            if($schedule_lineNo == $lineNo){
                if($_POST["mode"] == "overwrite"){
                    fwrite($fp,$new_line);
                }
                elseif($_POST["mode"] == "delete"){

                }
            else{
                fwrite($fp,$line);
            }
        }
        fclose($fp);
    }
?>

Answer 1

Don't over complicate things. Since you using file() function, and your feeding the line number desired, use that line number to designate which array key you will overwrite. Example:

$filename = "sample.txt";

function edit($filename, $lineNo){
    $new_line = "Hello";
    $schedule_list = file($filename, FILE_SKIP_EMPTY_LINES | FILE_IGNORE_NEW_LINES);
    if(!isset($schedule_list[$lineNo-1])) {
        return false;
    }

    if(/** overwrite **/) {
        // use the line number as key and use it on the array returned by file()
        $schedule_list[$lineNo - 1] = $new_line; // numeric indices start at zero
    } elseif(/** delete **/) {
        unset($schedule_list[$lineNo-1]);
    }

    file_put_contents($filename, implode("\n", $schedule_list));

    return true;
}

var_dump(edit($filename, 1));