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In PHP programming, constants are an important concept. A constant is a value that cannot be changed during the execution of a script. Unlike variables, its value cannot be modified once defined. PHP provides several built-in constants and allows developers to define their own constants. Sometimes, we need to retrieve all the constants defined in the current script. PHP offers a very convenient function get_defined_constants() to help us achieve this goal.
get_defined_constants() is a built-in PHP function that returns all the defined constants in the current script, including both PHP's built-in constants and user-defined constants. The function returns an associative array, where the keys are the names of the constants and the values are the corresponding constant values.
array get_defined_constants(bool $categorize = false)
$categorize (optional): This is a boolean parameter, defaulting to false. If set to true, get_defined_constants() will categorize the constants, such as PHP built-in constants, extension constants, etc. If set to false, all constants will be listed in the same array.
The following code example demonstrates how to use the get_defined_constants() function to retrieve all defined constants and print them:
<?php
// Retrieve all defined constants
$constants = get_defined_constants();
<p>// Output the constant list<br>
foreach ($constants as $name => $value) {<br>
echo "$name = $value\n";<br>
}<br>
?><br>
In the example above, we first call the get_defined_constants() function to retrieve all defined constants and store the result in the $constants array. Then we use a foreach loop to iterate over the array and output the names and values of the constants.
If you want to retrieve constants by category, you can set the $categorize parameter of get_defined_constants() to true. Below is an example of retrieving categorized constants:
<?php
// Retrieve categorized constants
$categorized_constants = get_defined_constants(true);
<p>// Output constants in each category<br>
foreach ($categorized_constants as $category => $constants) {<br>
echo "Category: $category\n";<br>
foreach ($constants as $name => $value) {<br>
echo " $name = $value\n";<br>
}<br>
}<br>
?><br>
In this example, get_defined_constants(true) returns the constants grouped by category. Common categories include Core (PHP core constants), Directive (PHP configuration directive constants), and others. This way, you can view constants more clearly within each category.
get_defined_constants() is useful in many scenarios, especially when you need to debug or review the constants in your PHP environment. Here are some common use cases:
Debugging Configuration Constants: When we have set many configuration constants in PHP, get_defined_constants() can quickly show the current values of those constants.
Viewing PHP Environment Information: Some constants are related to the PHP environment or extensions. Using this function can help us understand the configuration information of the current environment.
Dynamic Handling of Constants: When we need to dynamically handle constants based on different values, this function is very useful.
Performance Considerations: Although get_defined_constants() is very convenient, frequent calls in large applications might affect performance. It is best to use it only during debugging or when necessary.
Including Custom Constants: This function not only returns PHP built-in constants but also includes custom constants defined by developers. If you want to retrieve only built-in constants, you may need to filter them when using the function.
The get_defined_constants() function provides a simple and convenient way to retrieve all defined constants in PHP. This is very useful for debugging and analyzing constants in your code. By using this function properly, you can better manage and review constants, ensuring the flexibility and maintainability of your code.
