how to log a function error message code example

Example 1: how to create a logfile in php?

<?php
//Something to write to txt log
$log  = "User: ".$_SERVER['REMOTE_ADDR'].' - '.date("F j, Y, g:i a").PHP_EOL.
        "Attempt: ".($result[0]['success']=='1'?'Success':'Failed').PHP_EOL.
        "User: ".$username.PHP_EOL.
        "-------------------------".PHP_EOL;

//Save string to log, use FILE_APPEND to append.
file_put_contents('./log_'.date("j.n.Y").'.log', $log, FILE_APPEND);

Example 2: php error log

/usr/local/apache/logs/error_log