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

No. In PHP, you can only know a variable doesn't exist when you try to access it.

Consider:

if ($data = file('my_file.txt')) {
    if (count($data) >= 0)
        $line = reset($data);
}
var_dump($line);

You have to restructure your code so that all the code paths leads to the variable defined, e.g.:

$line = "default value";
if ($data = file('my_file.txt')) {
    if (count($data) >= 0)
        $line = reset($data);
}
var_dump($line);

If there isn't any default value that makes sense, this is still better than isset because you'll warned if you have a typo in the variable name in the final if:

$line = null;
if ($data = file('my_file.txt')) {
    if (count($data) >= 0)
        $line = reset($data);
}
if ($line !== null) { /* ... */ }

Of course, you can use isset¹ to check, at a given point, if a variable exists. However, if your code relies on that, it's probably poorly structured. My point is that, contrary to e.g. C/Java, you cannot, at compile time, determine if an access to a variable is valid. This is made worse by the nonexistence of block scope in PHP.

¹ Strictly speaking, isset won't tell you whether a variable is set, it tell if it's set and is not null. Otherwise, you'll need get_defined_vars.