How does PHP ZipArchive check the compression ratio of files in a compressed package?

PHP ZipArchive is a class used to create and decompress ZIP files. In applications, sometimes we need to know the compression ratio of each file in the compressed package to understand the compression effect and performance. This article will introduce how to use the PHP ZipArchive class to view the compression rate of files in a compressed package.

First, we need to create a ZipArchive object and open a ZIP file. The code is as follows:

$zip = new ZipArchive;
$zipFile = 'path/to/archive.zip';

if ($zip->open($zipFile) === true) {
    // 在这里实现对压缩包文件压缩率的查看
} else {
    echo '无法打开ZIP文件';
}

Next, we can iterate through all the files in the compressed package and calculate the compression ratio by getting the pre-compression and post-compression sizes of each file. The code is as follows:

$totalSizeBefore = 0;
$totalSizeAfter = 0;

for ($i = 0; $i < $zip->numFiles; $i++) {
    $fileName = $zip->getNameIndex($i);
    $stat = $zip->statIndex($i);
    $sizeBefore = $stat['size'];
    $sizeAfter = $stat['comp_size'];
    
    $totalSizeBefore += $sizeBefore;
    $totalSizeAfter += $sizeAfter;
    
    $compressionRate = ($sizeBefore - $sizeAfter) / $sizeBefore * 100; // 计算压缩率
    
    echo "文件名：{$fileName}<br/>";
    echo "压缩前大小：{$sizeBefore} bytes<br/>";
    echo "压缩后大小：{$sizeAfter} bytes<br/>";
    echo "压缩率：{$compressionRate}%<br/>";
    echo "<br/>";
}

$averageCompressionRate = ($totalSizeBefore - $totalSizeAfter) / $totalSizeBefore * 100 / $zip->numFiles; // 计算平均压缩率

echo "总压缩前大小：{$totalSizeBefore} bytes<br/>";
echo "总压缩后大小：{$totalSizeAfter} bytes<br/>";
echo "平均压缩率：{$averageCompressionRate}%<br/>";

$zip->close();

The above code first defines the $totalSizeBefore and $totalSizeAfter variables, which are used to calculate the total size of all files before and after compression. Then it loops through all the files in the compressed package, obtains the size before and after compression of each file, and calculates the compression ratio. Finally, the average compression ratio of all files is calculated and the total pre- and post-compression size is output.

Note that the above code is only suitable for obtaining the file compression ratio in an existing ZIP file. If you want to get the compression ratio of the file when creating the ZIP file, you can use the file_get_contents function to get the contents of the file before adding the file to the ZIP file, and then call the gzcompress function to compress, calculate the size before and after compression and calculate the compression ratio.

In general, by using the methods provided by the PHP ZipArchive class, we can easily view the compression ratio of the files in the compressed package. This feature not only helps to understand the compression effect of the compressed package, but also evaluates the compression performance and optimizes the compression algorithm.

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