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资源类型

资源是一种特殊变量，保存了到外部资源的一个引用。资源是通过专门的函数来建立和使用的。所有这些函数及其相应资源类型见附录。

Note: 资源类型是 PHP 4 引进的。

参见 get_resource_type()。

转换为资源

由于资源类型变量保存有为打开文件、数据库连接、图形画布区域等的特殊句柄，因此将其它类型的值转换为资源没有意义。

释放资源

由于 PHP4 Zend 引擎引进了引用计数系统，可以自动检测到一个资源不再被引用了（和 Java 一样）。这种情况下此资源使用的所有外部资源都会被垃圾回收系统释放。因此，很少需要手工释放内存。 Thanks to the reference-counting system introduced with PHP 4's Zend Engine, a resource with no more references to it is detected automatically, and it is freed by the garbage collector. For this reason, it is rarely necessary to free the memory manually.

Note: 持久数据库连接比较特殊，它们不会被垃圾回收系统销毁。参见数据库永久连接一章。

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PHP手册
PHP手册 - N: 资源类型

用户评论:

Soos Gergely (26-Apr-2010 01:24)

It is always wrong to assume that some operation, like casting to a resource makes no sense. People will always find some extreme case where it would be useful; like the previous example with mysql. My problem was that I wanted to start daemons from a web interface but the apache filehandles were inherited which caused that apache was unable to restart. If I could only typecast a number to a filehandle and then close it... Instead I had to write a small C program that closes every filehandle and then starts my program. I surely miss Apache2::SubProcess from perl. (Also, in perl you can reopen a file and then close it using IO::Handle module's fdopen. I'm just saying.)

wetmonkey__ at at __gmail dot com (16-Dec-2008 12:17)

Resources are commonly used to iterate through a mysql or file handle.
example

<?php
while($row = mysql_fetch_row($resource)){
  echo $row[0] ;
}
?>

It's possible to fake this treatment.

<?php
class fakewhile{

public $arrayCount;
public $arrayCounter;

function setArrValues(){
   $this->arrValues = array(0 =>array("apple","artichoke","apricot"),1 => array("bears","dogs","cats"));
  $this->arrayCounter = 0;
  $this->arrayCount = count($this->arrValues);
}

function outputValues(){
/*
 * Anything until the if statement is evaluted one more
 * time then the array count value
 */
 $arrayInfo = $this->arrValues;
 $arrCounter = $this->arrayCounter;
 if($arrCounter > $this->arrayCount){
  return false;
 }
 $endCounter = $arrCounter+1;
 $this->arrayCounter = $endCounter;
 return $arrayInfo[$arrCounter];
}

}

$fw = new fakewhile();
$fw->setArrValues();
while($row = $fw->outputValues()){
    print_r($row);
}
?>

Hopefully will get someone started on completing a complete application.

adrian dot dziubek at gmail dot com (07-Jul-2008 04:55)

I spent an hour trying to create mock setup for testing SQL queries. The explanation here, that a resource contains file handlers and therefore there is no sense in trying to create one is lame. Being unable to redefine functions, creating a fake resource was the second thing I tried to put test in place, but looking at the search results, I see I'm the first one to try... For me it looks like security by obscurity.