Editing Troubleshooting of PHP errors (section)

== Troubleshooting steps of PHP errors ==
Display error message or check the PHP error logs
* {{kbd | key=<nowiki>ini_set("display_errors", "On");</nowiki>}} See details on [http://php.net/manual/en/errorfunc.configuration.php PHP: Runtime Configuration - Manual]
* {{kbd | key=<nowiki>error_reporting(E_ALL);</nowiki>}} See details on [http://php.net/manual/en/function.error-reporting.php PHP: error_reporting - Manual]
* [https://www.jetbrains.com/help/phpstorm/event-log-tool-window.html Event Log - Help | PhpStorm] 

Check the Web service logs
# {{kbd | key=<nowiki>sudo tail /var/log/httpd/error.log</nowiki>}} if the web service logs was located at {{kbd | key=<nowiki>/var/log/httpd/error.log</nowiki>}}
# Example log: {{kbd | key=<nowiki>[Thu Nov 08 12:20:40.412630 2018] [:error] [pid 12769] [client x.x.x.x:4433] PHP Parse error:  syntax error, unexpected '$var' (T_VARIABLE) in /home/wwwroot/path/to/file.php on line 100</nowiki>}}
# Display partial source code: {{kbd | key=<nowiki>sed -n '990,110p;111q' /home/wwwroot/path/to/file.php</nowiki>}}<ref>[https://stackoverflow.com/questions/83329/how-can-i-extract-a-predetermined-range-of-lines-from-a-text-file-on-unix How can I extract a predetermined range of lines from a text file on Unix? - Stack Overflow]</ref>
# 檢查網站伺服器 error log e.g. 如果使用 [https://www.nginx.com/ NGINX] Web Server 可輸入指令 {{kbd | key=<nowiki>sudo tail /var/log/nginx/error.log</nowiki>}}

Simply the question
* Is the [http://php.net/manual/en/function.function-exists.php function_exists]? 
** Extension dependency? Install the extension you need.
** If not, looking for the alternative functions.
* Was the function really executed? Maybe using the __LINE__ to examin the logic.
* Disable the logical judgement and just print text using [http://php.net/manual/en/function.var-dump.php var_dump] or [http://php.net/manual/en/function.print-r.php print_r] functions.
* Check the if-else condition was satisfied or not cf: [http://www.leepoint.net/notes-java/data/strings/12stringcomparison.html Java: String Comparison] It's logical (compiler will not show the warning) but wrong.
* try & catch: [http://php.net/manual/en/language.exceptions.php PHP: Exceptions]

=== logging ===
native error logging
* [http://www.php.net/ PHP] log: check the configuration file: /etc/php.ini (the location of configuration file can be verified by [http://php.net/manual/en/function.phpinfo.php phpinfo()] )
(for production site) unmark theese lines in the php.ini and restart Apache service
<pre>
log_errors = On
error_log = "php_error.log"
</pre>
(for development site) using [http://php.net/manual/en/function.error-reporting.php error_reporting]
<pre>
error_reporting(E_ALL);
</pre>

[http://tw1.php.net/print_r PHP: print_r - Manual]
<pre>
$log = print_r($variable, true);
//save to the log file

$log = print_r(debug_backtrace(), true);
//Generates a backtrace and save to the log file
</pre>

capture the result of var_dump:
ob_start
* [http://stackoverflow.com/questions/139474/how-can-i-capture-the-result-of-var-dump-to-a-string php - How can I capture the result of var_dump to a string? - Stack Overflow]
* [http://php.net/manual/en/function.error-log.php PHP: error_log - Manual]
<pre>
ob_start();
var_dump($some_variable);
$result = ob_get_clean();
error_log($result, 3, 'd:/result.log');
</pre>

QuickForm
<pre>
$result = var_dump($some_variable);
$form->addElement('html', $result);
</pre>


[http://ellislab.com/codeigniter CodeIgniter]: [http://stackoverflow.com/questions/7370391/how-to-configure-codeigniter-to-report-all-errors php - How to configure Codeigniter to report all errors? - Stack Overflow]


show the line number and filename
<pre>
echo 'Houston, we've had a problem '. __line__ . ' ' . __FILE__ ."<br />";
</pre>
more on [http://php.net/manual/en/language.constants.predefined.php PHP: Magic constants], [https://github.com/Seldaek/monolog monolog]