有一段时间一直迷惑于PHP中引用的传递，后来查手册及C源程序，并反复测试，大致对引用传递在内存中的模式有了一定的了解，后来为了加深印象，写了个总结，应该不会有大的问题——当然这是在PHP4中，在以后的版本中可能会有变化。当时写总结的时候，想锻炼一下英语，因此就凑合了一篇。不过本人英语不好，也懒得翻译，反正当时想自己看得懂就行了。今天心血来潮，突然觉得还蛮有用的，于是在这里现丑了，请大家指正。那位看得懂的帮忙翻译一下吧，我没空了。
[code:1:2433d9e506]
<?php
/*
filename: SetGetTest.php
comment on assignment by value and referrence
assuming $var is a varialbe, its handle(pointer) is named as *var,
and its content is named as @var
the memory area of @var is referred by *var, if the *var is the same,
then the memory areas are the same, so *var is just like a pointer.
1. when $var = $var1
@var copied from @var1, but in the different memory area,
new *var assigned by the system, pointing to the memory area holding @var
*var and *var1 are different
2. when $var =& $var1,
*var assigned by *var1, and the @var is not assigned or copied,
it is absolutely the same as @var1, and in the same memory area
both *var and *var1 pointing to the memory area, that means they are the same.
passing by referrence
3.
function set1(&$s){
$var =& $s;
}
set1($var1) results:
*var1 passing to the function, and *s is the same as *var1,
then *var is the same as *s, the result is that *var is the same as *var1
and all the contents are the same obviously.
4.
function set2(&$s){
$var = $s;
}
set2($var1) results:
*var1 passing to the function, and *s is the same as *var1,
but when $var = $s executes, from 1. we can see @var is the same as @s,
but *var is different from *s, so @var and @s is not in the same memory area,
while @s and @var1 is sharing the same memory area, also *var1 and *s are the same.
5.
normal function return:
function get(){ return $var1; }
assuming the result is referred by a variable $result.
then @result is copied from @var1 but *result is not the same as *var1
when $var = get();
first you get a variable $result, as I said above, @result is the same as @var1, but *result
is different from *var1, and next $var = $result executes.
As I said in 1., you can find, @var is the same as @result and the same as @var1,
but *var is different from *result AND *var1;
while $var =& get() just means:
*var is the same as *result, so @var and @result are in the same memory area,
but they are still different from those of $var1,
both the memory area of @var1 and *var1,
6.
returning by referrence
function &get(){ return $var1; }
there are two ways to get the result
$var = get(); and $var =& get(); now I will tell the difference
I. $var = get();
the *result is the same as *var1 and so @result and @var1 are the same.
and then $var = $result executes,
*var is not the same as *result, and also different from *var1,
but their contents are the same.
I. $var =& get();
the *result is the same as *var1 and so @result and @var1 are the same.
and then $var =& $result executes,
this means $var and $result are the same, both of @ and *
*/
// the test is the following
function println($s = ""){
print "$s<br>\n";
}
class GetSetTest
{
var $var = null;
function setByRef(&$arg){
$this->var =& $arg;
}
function passByRef(&$arg){
$this->var = $arg;
}
function setByVal($arg){
$this->var = $arg;
}
function &getByRef(){
return $this->var;
}
function getByVal(){
return $this->var;
}
}
$o = new GetSetTest;
println("============ setByRef getByRef =============");
println("-----------------Before change----------------");
$in = "before change";
$o->setByRef($in);
$outByVal = $o->getByRef();
$outByRef =& $o->getByRef();
println("\$in: ".$in);
println("\$outByVal: ".$outByVal);
println("\$outByRef: ".$outByRef);
println("\$this->var: ".$o->var);
println("-----------------After change-----------------");
$in = "after change";
println("\$in: ".$in);
println("\$outByVal: ".$outByVal);
println("\$outByRef: ".$outByRef);
println("\$this->var: ".$o->var);
println();
println("============ setByRef getByVal =============");
println("-----------------Before change----------------");
$in = "before change";
$o->setByRef($in);
$outByVal = $o->getByVal();
$outByRef =& $o->getByVal();
println("\$in: ".$in);
println("\$outByVal: ".$outByVal);
println("\$outByRef: ".$outByRef);
println("\$this->var: ".$o->var);
println("-----------------After change-----------------");
$in = "after change";
println("\$in: ".$in);
println("\$outByVal: ".$outByVal);
println("\$outByRef: ".$outByRef);
println("\$this->var: ".$o->var);
println();
println("============ passByRef getByVal =============");
println("-----------------Before change----------------");
$in = "before change";
$o->passByRef($in);
$outByVal = $o->getByVal();
$outByRef =& $o->getByVal();
println("\$in: ".$in);
println("\$outByVal: ".$outByVal);
println("\$outByRef: ".$outByRef);
println("\$this->var: ".$o->var);
println("-----------------After change-----------------");
$in = "after change";
println("\$in: ".$in);
println("\$outByVal: ".$outByVal);
println("\$outByRef: ".$outByRef);
println("\$this->var: ".$o->var);
println();
/*
以下输出结果是我（夜猫子）擅自编辑添加的，主要是为后来人查看方便加在这里，越肉代庖，向longnetpro致歉
输出结果：
============ setByRef getByRef =============
-----------------Before change----------------
$in: before change
$outByVal: before change
$outByRef: before change
$this->var: before change
-----------------After change-----------------
$in: after change
$outByVal: before change
$outByRef: after change
$this->var: after change
============ setByRef getByVal =============
-----------------Before change----------------
$in: before change
$outByVal: before change
$outByRef: before change
$this->var: before change
-----------------After change-----------------
$in: after change
$outByVal: before change
$outByRef: before change
$this->var: after change
============ passByRef getByVal =============
-----------------Before change----------------
$in: before change
$outByVal: before change
$outByRef: before change
$this->var: before change
-----------------After change-----------------
$in: after change
$outByVal: before change
$outByRef: before change
$this->var: after change
*/
?>
[/code:1:2433d9e506]
| 夜猫子 回复于：2003-12-17 09:48:54 |
| 老兄你经常都发一些要我慢慢看的东西，呵呵，我先收，等闲了来拜读 |
| mikespook 回复于：2003-12-17 11:42:55 |
| 呼，好累~~~~没读代码~~~只看了前面的部分~~~ 恩，如果能和C++做一个比较就好了~~~~ 还有一点我不是很明白~~ $t="123"; funciton &test($t1) { $t2 = $t1 return $t2; } $t3 =& test($t); $t, $t1 ,$t2 内存都将在什么时候释放~~ |
| NightKids 回复于：2003-12-17 14:56:35 |
| 首先，ZEND 里面定义的两个函数 ZEND_API void start_memory_manager(TSRMLS_D); ZEND_API void shutdown_memory_manager(int silent, int clean_cache TSRMLS_DC); PHP5.0b2 在源代码 的 main.c 里面的 php_request_shutdown_for_exec 函数里有 1190 行 开始: [code:1:8988e926b5] void php_request_shutdown(void *dummy) { TSRMLS_FETCH(); /* EG(opline_ptr) points into nirvana and therefore cannot be safely accessed * inside zend_executor callback functions. */ EG(opline_ptr) = NULL; zend_try { zend_exec_finished(TSRMLS_C); } zend_end_try(); zend_try { php_end_ob_buffers((zend_bool)(SG(request_info).headers_only?0:1) TSRMLS_CC); } zend_end_try(); zend_try { sapi_send_headers(TSRMLS_C); } zend_end_try(); if (PG(modules_activated)) zend_try { php_call_shutdown_functions(); } zend_end_try(); if (PG(modules_activated)) { zend_deactivate_modules(TSRMLS_C); } zend_try { int i; for (i=0; i<NUM_TRACK_VARS; i++) { if (PG(http_globals)[i]) { zval_ptr_dtor(&PG(http_globals)[i]); } } } zend_end_try(); zend_deactivate(TSRMLS_C); zend_try { sapi_deactivate(TSRMLS_C); } zend_end_try(); zend_try { shutdown_memory_manager(CG(unclean_shutdown), 0 TSRMLS_CC); } zend_end_try(); zend_try { zend_unset_timeout(TSRMLS_C); } zend_end_try(); #ifdef PHP_WIN32 CoUninitialize(); #endif } /* }}} */ [/code:1:8988e926b5] shutdown_memory_manager(); 同样 其他方式 结束的时候 也会 调用 shutdown_memory_manager(); 也就是说释放是在 php 程序执行完毕，返回结果之后就释放了 |