what does this do

Talguy

Ok so i do understand php pretty good for a beginner. In a couple of tutorials I have I have worked with too build certain apps I have came across lines that look something like this:
@mkdir($dir,$mode) or this @mysql_fetch_array( $result )

so what I am asking is what does the @ symbol stand for in php.

thorpe

It supresses error messages.

So... if a call to the function foo() might produce an error, calling @() will hide that error.

The supressor is best avoided when possible however. Your best to change these setting using error_reporting().

Talguy

so it is a bad idea to the @ and just try like a catch instead and the report it

halojoy

it depends

@ will stop hackers to know what happens, for example filenames and filepaths at your website
that can be displayed in errors and warnings

while you are working yourself with your scripts, you might not use @,
because you WANT to KNOW what is happening if there is an error

so using @function()
is a matter of security

bradgrafelman

Or register your own error function to handle PHP's errors (display them nicely, log them, etc.). More info about error handling found here: [man]errorfunc[/man]. More information about the @ error control operator can be found here: [man]language.operators.errorcontrol[/man].

thorpe

@ will stop hackers to know what happens, for example filenames and filepaths at your website
that can be displayed in errors and warnings

And so will turning off error_reporting() or only logging errors. To be honest, I can't remember the last time I needed to use @. Im sure it was a shell script that I knew would throw an error even with error reporting off.

Avoid it if you can.

Jack_McSlay

it can be used in some cases to do what your code is actually supposed to do. for example, I once made a code using getimagesize() to get info from an image file and display it, and display an "image not found" if if coudn't find it. then I had to use @ to supress the error so it woudn't show the error on the page.

so basicaly you use it when you'll be using a function in a way which what would be interpreted by PHP is not an error at all according to your program.

if you're writing a proprietary code, you may just turn off error reporting on the beginning of the script after everything is ready, but in the case of distribution code, it could be a good idea to use it.

examancer

It can also be useful in situations where you know a statement may throw an error but whether or not that error occurs has no bearing on the rest of your script... Its something I use very sparingly, but it shows up a couple times even in some of my more robust web apps.

MarkR

I think @ is fine to suppress warnings / notices which would otherwise take down my app.

I use a custom error handler which aborts the page when any enabled error occurs, INCLUDING warning, notice, etc. This is very helpful as it ensures that my pages never charge headlong into oblivion.

As far as I'm concerned, NORMALLY, even an E_NOTICE is a bad thing.

However, occasionally I don't mind - the commonest is assigning something from a checkbox:

$blah = (bool) $_POST['checkbox'];

Which of course, would generate an E_NOTICE if the checkbox was not checked, due to nonexistent array element. So I do

$blah = (bool) @ $_POST['checkbox'];

Instead, safe in the knowledge that the @ will never be suppressing any important error, as that's pretty much the only thing which can fail.

It is a major problem using @ to do anything significant, e.g.

$f = @some_special_extension_function();
if ($f === FALSE) { // error handling ...
}

Sounds fine, until you realise that if the extension function was absent, a "Call to undefined function" fatal error will occur, but the @ will suppress it, resulting in a totally useless "blank page" problem which would prove difficult to diagnose.

Conclusion:

Using @ to suppress notices / warnings in an expression is OK.
Using @ when calling functions is bad.

Mark

Jack_McSlay

MarkR wrote:
Which of course, would generate an E_NOTICE if the checkbox was not checked, due to nonexistent array element. So I do
$blah = (bool) @ $_POST['checkbox'];

why not use

 $blah = isset ($_POST['checkbox']);

 $blah = !empty ($_POST['checkbox']);

that's what I do whenever I need to readlo checkbox values

Talguy

wow that is a lot of information an examples thanks everyone

Jack_McSlay

one last advice: don't EVER use @ before require or include. that will make your script to have the error reporting turned off during the entire included file, and if there's any errors on it, you'll have a hard time trying to find out what theheck is going on

examancer

Good advice. I wouldn't have thought that would occur. Thanks.