如何在PHP中高效處理大檔案而不導致記憶體耗盡？

Handling Large Files using PHP without Memory Exhaustion

Reading and processing large files in PHP can be challenging due to memory limitations. The file_get_contents() function can trigger a "Memory exhausted" error when dealing with large files that consume more memory than allowed.

Understanding Memory Allocation

When using file_get_contents(), the entire file is read and stored as a string in memory. For large files, this can exceed the allocated memory and lead to the error.

Alternative Approach: Chunked File Reading

To avoid this issue, consider using alternative methods such as fopen() and fread() to read the file in chunks. This allows you to process smaller sections of the file at a time, managing memory usage effectively. Here's a function that implements this approach:

<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($callback, [fread($handle, $chunk_size), &$handle, $i]);
            $i++;
        }
        fclose($handle);
        return true;
    } catch (Exception $e) {
        trigger_error("file_get_contents_chunked::" . $e->getMessage(), E_USER_NOTICE);
        return false;
    }
}</code>

Example Usage

To use this function, define a callback that handles the chunk and provide the necessary parameters:

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

Additional Considerations

Another optimization is to avoid using complex regular expressions, which can consume significant memory when applied to large inputs. Consider using native string functions like strpos, substr, and explode instead.

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