Support for caching results (patch included)

```
I don't think it's a good idea to process the spreadsheet file over and over
again, especially as it
may not change very frequently.

Here's a little function to cache the results of the spreadsheet read as a PHP
object. Make sure
you create the cache directory and make sure it can be written to.

best,
matt

function Cached_Spreadsheet($filename) {
$cache_dir = './cache'; //set to null to disable cache
$xlsmtime = filemtime($filename);
$cached = false;

// If CACHE ENABLED
if ($cache_dir != '' && file_exists($cache_dir)) {
$cache_file = $cache_dir . '/xlscache_' . md5($filename);
$timediff = @($xlsmtime != filemtime($cache_file));
if ($timediff && file_exists($cache_file)) {
// cached file is fresh enough, return cached array
$result = unserialize(join('', file($cache_file)));
// set 'cached' to 1 only if cached file is correct
if ($result) $cached = true;
} else {
// cached file is too old, create new
$result = new Spreadsheet_Excel_Reader($filename, false);
$serialized = serialize($result);
if ($f = @fopen($cache_file, 'w')) {
fwrite ($f, $serialized, strlen($serialized));
fclose($f);
}
if ($result) $cached = false;
}
} else {
// If CACHE DISABLED >> load and parse the file directly
$result = new Spreadsheet_Excel_Reader($filename, false);
if ($result) $cached = false;
}

if ($cached) echo "\n";

// return result
return $result;
}

$xls = Cached_Spreadsheet("example.xls");
```

Original issue reported on code.google.com by `matt.sep...@gmail.com` on 11 Mar 2009 at 3:53

Attachments:
- [example-cached.php](https://storage.googleapis.com/google-code-attachments/php-excel-reader/issue-12/comment-0/example-cached.php)
- [php-excel-reader-2.zip](https://storage.googleapis.com/google-code-attachments/php-excel-reader/issue-12/comment-0/php-excel-reader-2.zip)

Review the attached example-cached.php and php-excel-reader-2.zip, then compare the proposed Cached_Spreadsheet usage with the current reader entry point. Done means repeated reads can reuse a writable cache, changes to the spreadsheet invalidate it, and disabling or unavailable caching still loads the file directly.

Written by the indexing model from the issue text.