Error Suppression @ Not Working

Question

I've been happily using the error suppression operator on my PHP dev setup. But recently have gotten hit with Notices like so:

Notice: Uninitialized string offset: 0 in C:\websites\xxx\htdocs\includes\myscript.php on line 35

Line 35:

$file_name = @$File['file_name'];

I have display_errors on, and error_reporting set to 6143 (E_ALL).

Am I missing something? Shouldn't the error be suppressed?

Edit:

Tested in virgin script:

$a = array();
$b = @$a['f5'];

Suppressed the error. So I'm thinking we're changing the error_reporting value somehow. (Film at 11)

Thx for yr help.

Answer 1

Not a big fan of error suppression here except for throw-away scripts or instances where there really is no good way to catch an error.

Let me explain the behavior of the Uninitialized string offset error. It's not a bug:

Example #1

$a = 0;
$b = $a['f5'];

$a is a numeric scalar value. In the second line PHP is implicitly casting this numeric value to a string. The string '0' has a length of 1.

In PHP you can lookup a character in a string using an array index, as PHP stores strings as arrays internally. For instance:

$s= 'abcd';
print_r($s[1]);

The output of this code will be b as it is the second character in the string. In example #1 the lookup 'f5' is being converted to a number as strings can only be indexed by character position. echo intval('f5'); shows us what PHP interprets the 'f5' string as 0 in a numeric context.

With me so far? Here's what happens when we apply this to example #2

Example #2

$a = '';
$b = $a['f5'];

$a is zero-length string. The second line is the same as $b= $a[0]; - i.e., the second line is asking for the first character of a zero-length string, but the string contains no characters. So PHP throws the following error, letting you know the index simply does not exist:

Notice: Uninitialized string offset: 0 in C:\websites\tcv3\wc2009\htdocs\aatest_array.php on line 3

These are the hard knocks of programming in a loosely typed language.

Answer 2

No, the @ suppressor avoids showing warnings from function calls, not variable access and declarations. The Notice is telling you that you are accessing a string element [0] that is not defined, thus not initialized. If you want to suppress these, try to check for all uninitialized variables and give them a value according, as you may do it with C.

Answer 3

Since the error involves a string offset of 0, it must not apply to the line of code provided. There is no integer offset; you're using the string 'file_name' there.

Also, using '@' is a really terrible idea. Functions can fail, causing the script to exit with absolutely no indication as to where or why. A better way to handle the line of code you've pasted is this:

if (isset($File['file_name'])) {
  $file_name = $File['file_name'];
} else {
  // throw exception, return FALSE, print an error and exit, whatever
}

Answer 4

OK, here's the thing: PHP doesn't deal well with subscripts to non-array vars. For instance:

$a = 0;
$b = $a['f5'];

Doesn't generate an error.

Whereas:

$a = '';
$b = $a['f5'];

Generates this error:

Notice: Uninitialized string offset: 0 in C:\websites\tcv3\wc2009\htdocs\aatest_array.php on line 3

And that's the problem I was having. If I switch it around to initializing $a with array(), the error suppression works. Moreover, without error suppression it gives the proper index in the error.

I suspect this is a bug in PHP 5.2.2. Can someone test this in a more up to date version?

Thx for your help guys.