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When working with ZIP files in PHP, we often use the zip_read() function to read entries from a compressed archive. However, many beginners notice that this function does not return an object or an array, but rather a "resource type" (resource). This leaves many developers wondering: why was PHP designed this way? What is the reasoning behind this design? This article will delve into this issue.
A resource type in PHP is a special data type that represents a handle to an external resource. Common examples of resource types include file handles, database connections, image handles, and more. A resource does not contain data itself, but rather is a reference to an underlying system resource.
Characteristics of a resource type:
Resources are managed internally by PHP.
Resources cannot be manipulated directly like arrays or objects.
After using a resource, it is necessary to call the corresponding close or release function, such as fclose().
The zip_read() function is designed to efficiently read entries from a compressed ZIP file. It is part of the lower-level interface of PHP's ZIP extension.
$zip = zip_open("http://m66.net/example.zip");
if (is_resource($zip)) {
while ($zip_entry = zip_read($zip)) {
echo "Entry name: " . zip_entry_name($zip_entry) . "\n";
}
zip_close($zip);
}
In the code above, zip_open() returns a resource type representing the open handle for the ZIP file, while zip_read() also returns a resource type representing the current ZIP entry being read.
There are several key reasons for returning a resource rather than an object or an array:
Resources are lightweight handles, and PHP's internal management of resources is more memory-efficient than objects. This design significantly reduces performance overhead, especially when dealing with large compressed files.
The zip_read() function is an older function that was implemented based on the low-level interfaces of the C library. At the time of its design, PHP's object model was not as mature, and using resource types aligned better with the implementation style of that era.
Resource types allow developers to manipulate the contents of the compressed archive more flexibly. By using multiple related functions (such as zip_entry_open(), zip_entry_read(), and zip_entry_close()), developers can step through the data, offering greater control over the process.
While resource types are efficient, they are not as intuitive to work with and are prone to errors. After PHP 5.2, it is recommended to use the ZipArchive class to handle ZIP files, which provides a more modern and user-friendly object-oriented approach.
Example:
$zip = new ZipArchive();
if ($zip->open('http://m66.net/example.zip') === TRUE) {
for ($i = 0; $i < $zip->numFiles; $i++) {
echo "Entry name: " . $zip->getNameIndex($i) . "\n";
}
$zip->close();
}
The advantages of using ZipArchive:
Returns an object, making the code more readable and maintainable.
Encapsulates more useful methods.
Includes built-in error handling.
The zip_read() function returns a resource type because it was designed to be a low-level, lightweight, and efficient interface.
Resource types make it easier for PHP to manage low-level system resources, saving memory and enhancing performance.
However, this design comes with the drawback of being harder to use and more error-prone.
Modern PHP development recommends using the ZipArchive class, which is more intuitive and feature-rich.
Understanding the reasoning behind this design can help us make better decisions when choosing which ZIP handling interface to use in PHP.
