PHP and undefined variables strategy

Question

I am a C++ programmer starting with PHP. I find that I lose most of the debugging time (and my selfesteem!) due to undefined variables. From what I know, the only way to dea

Answer 1

Personally, I try and set variables, even if it's with an empty string, array, Boolean, etc. Then I use a function such as isset() before using them. For example:

$page_found = false;

if ($page_found==false) {
    // Do page not found stuff here
}

if (isset($_POST['field'])) {
    $value = $_POST['field'];
    $sql = "UPDATE table SET field = '$value'";
}

And so on. And before some smart-ass says it: I know that query's unsafe. It was just an example of using isset().

Answer 2

Good practice is to define all variable before use, i.e., set a default value:

$variable = default_value;

This will solve most problems. As suggested before, use Xdebug or built-in debugging tools in editors like NetBeans.

Answer 3

This is a common complaint with PHP. Here are some ideas:

1. Use a code analysis tool. Many IDEs such as NetBeans will help also.

2. Just run the code. PHP doesn't have an expensive compilation step like C++ does.

3. Use unit testing. Common side effects include: better code.

4. Set error_reporting(-1), or the equivalent in your ini file.

5. Get xdebug. It's not preventative, but stack traces help with squishing bugs.

6. isset(), === null (identity operator), and guard clauses are your friends.

Loose and dynamic typing are a feature of the language. Just because PHP isn't strict about typing doesn't mean you can't be. If it really bugs you and you have a choice, you could try Python instead—it's a bit stricter with typing.

Answer 4

I really didn't find a direct answer already here. The actual solution I found to this problem is to use PHP Code Sniffer along with this awesome extension called PHP Code Sniffer Variable Analysis.

Also the regular PHP linter (php -l) is available inside PHP Code Sniffer, so I'm thinking about customizing my configuration for regular PHP linting, detecting unused/uninitialized variables and validating my own code style, all in one step.

My very minimal PHPCS configuration:

<?xml version="1.0"?>
<ruleset name="MyConfig">
    <description>Minimal PHP Syntax check</description>
    <rule ref="Generic.PHP.Syntax" />
    <rule ref="VariableAnalysis" />
</ruleset>

Answer 5

From what I know the only way to deal with them is to watch the output at execution time.

Not really: To prevent these notices from popping up, you just need to make sure you initialize variables before accessing them the first time. We (sadly IMO) don't have variable declaration in PHP, but initializing them in the beginning of your code block is just as well:

$my_var = value;

Using phpDocumentor syntax, you can also kind of declare them to be of a certain a type, at least in a way that many IDEs are able to do code lookup with:

/** @desc optional description of what the variable does
    @var int */
$my_var = 0;

Also, you can (and sometimes need to) use isset() / empty() / array_key_exists() conditions before trying to access a variable.

I agree this sucks big time sometimes, but it's necessary. There should be no notices in finished production code - they eat up performance even if displaying them is turned off, plus they are very useful to find out typos one may have made when using a variable. (But you already know that.)

Answer 6

I believe that various of the Code Coverage tools that are available for PHP will highlight this.