對大檔案使用 file_get_contents() 時如何避免記憶體耗盡錯誤？

File_get_contents Memory Exhaustion: A Comprehensive Solution

When dealing with large file processing, the infamous PHP Fatal error: Allowed memory exhausted error can be a recurring issue. This problem arises when file_get_contents() attempts to read the entire contents of a sizeable file into memory, often exceeding the allocated memory limit.

Alternative to file_get_contents()

Instead of loading the entire file into memory, a more efficient approach is to open the file as a pointer and read it in smaller chunks using fread(). This allows for memory management, which is critical for handling large files.

Below is a custom function that mimics the functionality of Node.js's file processing API:

<code class="php">function file_get_contents_chunked($file, $chunk_size, $callback)
{
    try {
        $handle = fopen($file, "r");
        $i = 0;
        while (!feof($handle)) {
            call_user_func_array($callback, array(fread($handle, $chunk_size), &$handle, $i));
            $i++;
        }
    } catch (Exception $e) {
        trigger_error("file_get_contents_chunked::" . $e->getMessage(), E_USER_NOTICE);
        return false;
    }
    fclose($handle);

    return true;
}</code>

This function accepts three parameters: the file path, the desired chunk size, and a callback function that will be called for each chunk read.

Usage of Custom Function

The file_get_contents_chunked() function can be used as follows:

<code class="php">$success = file_get_contents_chunked("my/large/file", 4096, function ($chunk, &$handle, $iteration) {
    /* Process the chunk here... */
});</code>

Regex Considerations

Performing multiple regex operations on a large chunk of data is inefficient. Consider using native string manipulation functions like strpos(), substr(), trim(), and explode().

Example Cleanup

Instead of:

<code class="php">$newData = str_replace("^M", "", $myData);</code>

Use:

<code class="php">$pattern = '/\r\n/';
$replacement = '';
$newData = preg_replace($pattern, $replacement, $myData);</code>

By utilizing the aforementioned techniques, it is possible to effectively process large files without encountering memory exhaustion errors.

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