好吧，如果物理內存是有限的（你看到的致命錯誤:)
Fatal error: Allowed memory size of 536870912 bytes exhausted
我會建議做磁盤上的輸出緩衝（見ob_start回調參數）。輸出緩衝工作分塊，這意味着，如果仍然有足夠的內存將單個塊保存在內存中，則可以將其存儲到臨時文件中。
// handle output buffering via callback, set chunksize to one kilobyte
ob_start($output_callback, $chunk_size = 1024);
但是，您必須記住，這隻會防止緩衝時出現致命錯誤。如果您現在想要返回緩衝區，則仍需要有足夠的內存或您可以返回文件句柄或文件路徑，以便還可以對輸出進行流式處理。
但是，您可以使用該文件，然後獲取所需的字節大小。 PHP字符串的開銷並不多，所以如果仍然有足夠的內存用於文件大小，這應該很好。你可以減去偏移量來獲得一個小房間並且玩起來很安全。只是嘗試和錯誤一點點。
一些示例代碼（PHP 5.4）：
<?php
/**
* @link http://stackoverflow.com/questions/5446647/how-can-i-use-var-dump-output-buffering-without-memory-errors/
*/
class OutputBuffer
{
/**
* @var int
*/
private $chunkSize;
/**
* @var bool
*/
private $started;
/**
* @var SplFileObject
*/
private $store;
/**
* @var bool Set Verbosity to true to output analysis data to stderr
*/
private $verbose = true;
public function __construct($chunkSize = 1024) {
$this->chunkSize = $chunkSize;
$this->store = new SplTempFileObject();
}
public function start() {
if ($this->started) {
throw new BadMethodCallException('Buffering already started, can not start again.');
}
$this->started = true;
$result = ob_start(array($this, 'bufferCallback'), $this->chunkSize);
$this->verbose && file_put_contents('php://stderr', sprintf("Starting Buffering: %d; Level %d\n", $result, ob_get_level()));
return $result;
}
public function flush() {
$this->started && ob_flush();
}
public function stop() {
if ($this->started) {
ob_flush();
$result = ob_end_flush();
$this->started = false;
$this->verbose && file_put_contents('php://stderr', sprintf("Buffering stopped: %d; Level %d\n", $result, ob_get_level()));
}
}
private function bufferCallback($chunk, $flags) {
$chunkSize = strlen($chunk);
if ($this->verbose) {
$level = ob_get_level();
$constants = ['PHP_OUTPUT_HANDLER_START', 'PHP_OUTPUT_HANDLER_WRITE', 'PHP_OUTPUT_HANDLER_FLUSH', 'PHP_OUTPUT_HANDLER_CLEAN', 'PHP_OUTPUT_HANDLER_FINAL'];
$flagsText = '';
foreach ($constants as $i => $constant) {
if ($flags & ($value = constant($constant)) || $value == $flags) {
$flagsText .= (strlen($flagsText) ? ' | ' : '') . $constant . "[$value]";
}
}
file_put_contents('php://stderr', "Buffer Callback: Chunk Size $chunkSize; Flags $flags ($flagsText); Level $level\n");
}
if ($flags & PHP_OUTPUT_HANDLER_FINAL) {
return TRUE;
}
if ($flags & PHP_OUTPUT_HANDLER_START) {
$this->store->fseek(0, SEEK_END);
}
$chunkSize && $this->store->fwrite($chunk);
if ($flags & PHP_OUTPUT_HANDLER_FLUSH) {
// there is nothing to d
}
if ($flags & PHP_OUTPUT_HANDLER_CLEAN) {
$this->store->ftruncate(0);
}
return "";
}
public function getSize() {
$this->store->fseek(0, SEEK_END);
return $this->store->ftell();
}
public function getBufferFile() {
return $this->store;
}
public function getBuffer() {
$array = iterator_to_array($this->store);
return implode('', $array);
}
public function __toString() {
return $this->getBuffer();
}
public function endClean() {
return ob_end_clean();
}
}
$buffer = new OutputBuffer();
echo "Starting Buffering now.\n=======================\n";
$buffer->start();
foreach (range(1, 10) as $iteration) {
$string = "fill{$iteration}";
echo str_repeat($string, 100), "\n";
}
$buffer->stop();
echo "Buffering Results:\n==================\n";
$size = $buffer->getSize();
echo "Buffer Size: $size (string length: ", strlen($buffer), ").\n";
echo "Peeking into buffer: ", var_dump(substr($buffer, 0, 10)), ' ...', var_dump(substr($buffer, -10)), "\n";
輸出：
STDERR: Starting Buffering: 1; Level 1
STDERR: Buffer Callback: Chunk Size 1502; Flags 1 (PHP_OUTPUT_HANDLER_START[1]); Level 1
STDERR: Buffer Callback: Chunk Size 1503; Flags 0 (PHP_OUTPUT_HANDLER_WRITE[0]); Level 1
STDERR: Buffer Callback: Chunk Size 1503; Flags 0 (PHP_OUTPUT_HANDLER_WRITE[0]); Level 1
STDERR: Buffer Callback: Chunk Size 602; Flags 4 (PHP_OUTPUT_HANDLER_FLUSH[4]); Level 1
STDERR: Buffer Callback: Chunk Size 0; Flags 8 (PHP_OUTPUT_HANDLER_FINAL[8]); Level 1
STDERR: Buffering stopped: 1; Level 0
Starting Buffering now.
=======================
Buffering Results:
==================
Buffer Size: 5110 (string length: 5110).
Peeking into buffer: string(10) "fill1fill1"
...string(10) "l10fill10\n"
你得到與'print_r'，同樣的問題，出於好奇？如果沒有，你是否看到很多遞歸通知？ – Charles 2011-03-27 01:42:59
@Charles，可能不是。我*可以*使用'print_r'或'var_export'，但我真的很喜歡這個事實，我可以保留'var_dump'提供的變量類型和長度信息。當xdebug可用時，也增加了格式化好處。 – 2011-03-27 01:45:16
由於遞歸，這可能是無限量的輸出。嘗試在相同的變量上自己調用它，而不使用輸出緩衝來查看會發生什麼。 – Jon 2011-03-27 01:45:37