What are some common pitfalls to avoid when passing and manipulating variables across different PHP documents for a cohesive output?

One common pitfall to avoid when passing and manipulating variables across different PHP documents is not properly sanitizing user input, which can lead to security vulnerabilities such as SQL injection or cross-site scripting attacks. To solve this, always validate and sanitize user input before using it in your code. 

// Example of validating and sanitizing user input
$user_input = $_POST['user_input'];
$clean_input = filter_var($user_input, FILTER_SANITIZE_STRING);
```

Another common pitfall is not properly checking for the existence of variables before using them, which can result in undefined variable errors. To avoid this, always check if a variable is set before trying to access its value.

```php
// Example of checking if a variable is set before using it
if(isset($_GET['variable_name'])) {
    $variable = $_GET['variable_name'];
    // continue with processing the variable
} else {
    // handle the case when the variable is not set
}
```

Lastly, avoid using global variables excessively as they can make your code harder to maintain and debug. Instead, consider passing variables as function parameters or using classes and objects to encapsulate data.

```php
// Example of passing variables as function parameters
function process_data($data) {
    // process the data here
}

// Call the function and pass the variable
$data = $_POST['data'];
process_data($data);

Keywords

variable passing variable manipulation PHP documents cohesive output error handling

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