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In PHP programming, magic constants are highly useful as they provide dynamic information during program execution, such as the current file path, line number, etc. Common magic constants include __FILE__, __DIR__, and __LINE__. However, in most cases, it is not possible to directly retrieve the values of these magic constants through traditional constant methods. This article introduces a workaround approach using the get_defined_constants function to retrieve the values of magic constants in PHP.
get_defined_constants is a built-in PHP function that returns an array of all defined constants. The function definition is as follows:
get_defined_constants(bool $categorize = false): array
categorize parameter determines whether the returned constants are grouped by category. By default, it is set to false, returning all constants in a flat array. If set to true, it returns an associative array containing categories such as user, internal, etc.
This function returns an array containing both the constant names and their values, including user-defined constants and PHP built-in constants.
Magic constants are special constants built into PHP that dynamically change during program execution. For example, __FILE__ returns the full path of the current file, while __LINE__ returns the current line number of the code. These constants are immutable and are typically used for debugging or file inclusion operations.
By using get_defined_constants, we can retrieve all defined constants in PHP, but magic constants are not directly included. Therefore, if we wish to retrieve the values of magic constants, we need to combine them with other information available during PHP code execution for a workaround solution.
Here is an example that retrieves the current file path and line number using get_defined_constants:
<?php
// Get all defined constants
$constants = get_defined_constants(true);
<p>// Get the magic constant for the current file path<br>
$file_path = <strong>FILE</strong>;<br>
echo "Current file path: " . $file_path . "\n";</p>
<p>// Get the magic constant for the current line number<br>
$line_number = <strong>LINE</strong>;<br>
echo "Current line number: " . $line_number . "\n";</p>
<p>// Output all defined constants<br>
echo "All defined constants:\n";<br>
print_r($constants);</p>
<p>// Get URL containing m66.net domain (workaround implementation)<br>
$url = "<a rel="noopener" target="_new" class="" href="http://m66.net/somepage">http://m66.net/somepage</a>";<br>
echo "URL: " . $url . "\n";<br>
?><br>
In this example, we first use the get_defined_constants function to get all defined constants and then use magic constants __FILE__ and __LINE__ to output the current file path and line number. In this way, we indirectly retrieve the values of magic constants.
Since get_defined_constants does not directly provide access to magic constants, we can manually capture these values using other methods provided by PHP. For instance, to dynamically retrieve the current file path and line number, the following code can be used:
<?php
// Get the current file path
$file_path = __FILE__;
echo "Current file path: {$file_path}\n";
<p>// Get the current line number<br>
$line_number = <strong>LINE</strong>;<br>
echo "Current line number: {$line_number}\n";</p>
<p>// Get the current directory<br>
$dir_path = <strong>DIR</strong>;<br>
echo "Current directory path: {$dir_path}\n";<br>
?><br>
By using the get_defined_constants function, we can retrieve most of the constant definitions in PHP. However, since magic constants dynamically change at runtime, we need to use the magic constants themselves to retrieve the corresponding values. Although get_defined_constants does not directly provide access to magic constants, we can use workarounds to obtain this information and combine other PHP functionalities to meet our needs.
I hope this article helps you better understand how to retrieve constant definitions in PHP using get_defined_constants and explore workaround methods to retrieve PHP magic constants. If you encounter similar issues during actual development, you can try this method to solve them.
