log error in php

if(!function_exists('log_error')){
    function log_error($error){
        $log_file = 'error_log.txt';
        $log = fopen($log_file, 'a');
        fwrite($log, date('Y-m-d H:i:s') . ' ' . $error . PHP_EOL);
        fclose($log);
    }
}

Example

log_error("Connection failed: " . $conn);