PHP Language - How to trap for error on COM instantiation

Author

How to trap for error on COM instantiation

Csaba Gabor

2005-04-22, 3:57 pm

The usual example shown for trapping for failure of COM instantiation
(Windows systems) is something like (see for example
http://at2.php.net/manual/en/class.com.php):

$word = new COM("word.application") or
die("Unable to instantiate Word");

This is all well and good, but if you are using a command
line interface (CLI) version of PHP 5 then you might wish to
have a little more sophisticated error handling. Specifically,
I have a function that looks like so:

function getWinDir() {
$result = "";
$oScript = new COM("MSScriptControl.ScriptControl");
...
return $result;
}

How do I trap for a COM instantion error here? In particular,
if it errors, I want to return ":Error" so the calling function
can deal with it. I do not want the program to abort. Nothing
I've tried seems to work. For example, suppose I'm having a bad
spelling day and leave off the final l to ensure an error.
If I insert an @ in the line, it will suppress the error reporting
and the program will also halt. And PHP doesn't like me trying

$oScript = new COM("MSScriptControl.ScriptContro") or
($result = ":Error");

I've also tried using set_error_handler and changing the
error level reporting with error_reporting and varying
$oldIni = ini_set("com.autoregister_verbose", 0); // $oldIni is 1
none of which has produced any joy.

Whenever the @ is there, I get a silent failure and a full stop.
If it's missing it also stops with the following message:
Fatal error: Uncaught exception 'com_exception' with message
'Failed to create COM object `MSScriptControl.ScriptContro':
Invalid syntax' in C:\Testing\DirFind.php:18

Thanks for any tips,
Csaba Gabor from Vienna

2005-04-22, 3:57 pm

Csaba Gabor wrote:
>
> I have a function that looks like so:
>
> function getWinDir() {
> $result = "";
> $oScript = new COM("MSScriptControl.ScriptControl");
> ...
> return $result;
> }
>
> How do I trap for a COM instantion error here?

In PHP 5, potentially fatal COM errors result in the COM
extension throwing instances of the class com_exception.
So your script needs to catch those exceptions:

function getWinDir() {
try {
$oScript = new COM("MSScriptControl.ScriptControl");
$oScript->call_a_method();
$oScript->call_another_method();
...
return $result;
} catch (com_exception $e) {
return array('errorCode' => $e->getCode(),
'errorMessage' => $e->getMessage(),
'errorFile' => $e->getFile(),
'errorLine' => $e->getLine());
}
}

Cheers,
NC

Csaba Gabor

2005-04-23, 3:55 pm

NC wrote:
> In PHP 5, potentially fatal COM errors result in the COM
> extension throwing instances of the class com_exception.
> So your script needs to catch those exceptions:
>
> function getWinDir() {
> try {
> ...
> } catch (com_exception $e) {
....
> }
> }

NC,

thank you, Thank You, THANK YOU! This was a majorly
nice way to go into the w

end. I had seen the comment
about Exceptions in http://php.net/com but I never used this
try / catch construct in PHP before and glossed over it.
Thanks again for pointing it out.

I have a follow up question about try / catch in general.
Is there a way (this has nothing to do with COM) that I can
use this contruct to catch all errors in the same place?

Example: the following code strikes me as an inelegant
workaround. Really, I'm looking for a default catch_all.

$err = ":Error";
try {
... some code which might error in unknown ways ...
$err = ""
} catch (Exception $e) { // this line doesn't work (it's ignored)
// since we haven't defined Exception, we'll never wind up here
}
if ($err) { // hacky was of compensating
// evidently, there was an error
}

Thanks,
Csaba

2005-04-24, 8:55 pm

2005-04-25, 3:56 pm

Csaba Gabor wrote:
>
> I have a follow up question about try / catch in general.
> Is there a way (this has nothing to do with COM) that I can
> use this contruct to catch all errors in the same place?

Yes. You can throw your own exception and catch it later.

> Example: the following code strikes me as an inelegant
> workaround. Really, I'm looking for a default catch_all.
>
> $err = ":Error";
> try {
> ... some code which might error in unknown ways ...
> $err = ""
> } catch (Exception $e) { // this line doesn't work (it's ignored)
> // since we haven't defined Exception, we'll never wind up here
> }
> if ($err) { // hacky was of compensating
> // evidently, there was an error
> }

This can be replaced with something like this:

try {
// ... some code which might error in unknown ways ...
if ($something_is_wrong) {
$error_message = 'Error: Something is wrong...';
$error_code = 666;
throw new Exception($error_message, $error_code);
}
} catch (Exception $e) {
// Now you can catch your own exception just as you
// would be catching any other...
}

Cheers,
NC

2005-04-28, 8:56 am

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