PHP passes function arguments by value by default, meaning changes to a variable inside a function do not affect it outside. To pass by reference, use an ampersand when calling the function so changes inside the function also change the variable outside. References in PHP are not like pointers in C - they are aliases and do not represent memory addresses. PHP uses copy-on-write and reference counting to manage memory, only copying variable values when they are changed.

1. PHP
PHP

2. PHP

3. PHP
By default, function arguments are passed by value (so that
if the value of the argument within the function is changed, it
does not get changed outside of the function).
http://php.net/manual/en/functions.arguments.php

4. PHP
<?php
function foo($var)
{
$var++;
}
$a=5;
foo($a);
// $a is 5 here

5. C

6. C ?
void foo(int var)
{
var++;
}
void main()
{
int a = 5;
foo(a);
/* a is 5 here */
}

7. PHP
You can pass a variable by reference to a function so the
function can modify the variable. The syntax is as follows:
http://php.net/manual/en/language.references.pass.php

8. PHP
<?php
function foo(&$var)
{
$var++;
}
$a=5;
foo($a);
// $a is 6 here

9. C

10. C ?
void foo(int* var)
{
(*var)++;
}
void main()
{
int a = 5;
foo(&a);
/* a is 6 here */
}

11. PHP
References in PHP are a means to access the same
variable content by different names. They are not like C
pointers; for instance, you cannot perform pointer arithmetic
using them, they are not actual memory addresses, and so
on.
http://php.net/manual/en/language.references.whatare.php

12. C ……

13. C ?
References in PHP are a means to access the same variable
content by different names. They are not like C pointers;
for instance, you cannot perform pointer arithmetic using
them, they are not actual memory addresses, and so on.
http://php.net/manual/en/language.references.whatare.php

14. C ?

15. PHP

16. C ???

17. PHP copy-on-write
PHP is a dynamic, loosely typed language, that uses copy-
on-write and reference counting.
http://php.net/manual/en/internals2.variables.intro.php

18. C ?

19. PHP

20. C ???

21. PHP

22. C
PHP :
:

23. PHP
typedef struct _zval_struct {
zvalue_value value; /* variable value */
zend_uint refcount__gc; /* reference counter
zend_uchar type; /* value type */
zend_uchar is_ref__gc; /* reference flag */
} zval;
is_ref__gc = PHP &

24. PHP
PHP
PHP copy-on-write

25. <?php
$a = 100;
xdebug_debug_zval('a');
//==> a: (refcount=1, is_ref=0)=100

26. <?php
$a = 100;
$b = $a;
xdebug_debug_zval('a');
xdebug_debug_zval('b');
//==> a: (refcount=2, is_ref=0)=100
//==> b: (refcount=2, is_ref=0)=100
$a $b (refcount )

27. <?php
$a = 100;
$b = $a;
$c = $a;
xdebug_debug_zval('a');
xdebug_debug_zval('b');
xdebug_debug_zval('c');
//==> a: (refcount=3, is_ref=0)=100
//==> b: (refcount=3, is_ref=0)=100
//==> c: (refcount=3, is_ref=0)=100

28. $a
<?php
$a = 100;
$b = $a;
$c = $a;
$a++;
xdebug_debug_zval('a');
xdebug_debug_zval('b');
xdebug_debug_zval('c');
//==> a: (refcount=1, is_ref=0)=101
//==> b: (refcount=2, is_ref=0)=100
//==> c: (refcount=2, is_ref=0)=100
$a
$b $c
copy-on-write

29. $c
<?php
$a = 100;
$b = $a;
$c = $a;
$a++;
unset($c);
xdebug_debug_zval('a');
xdebug_debug_zval('b');
xdebug_debug_zval('c');
//==> a: (refcount=1, is_ref=0)=101
//==> b: (refcount=1, is_ref=0)=100
//==> c: no such symbol
refcount

30. PHP

31. <?php
$a = 100;
xdebug_debug_zval('a');
//==> a: (refcount=1, is_ref=0)=100

32. <?php
$a = 100;
$b = &$a;
xdebug_debug_zval('a');
xdebug_debug_zval('b');
//==> a: (refcount=2, is_ref=1)=100
//==> b: (refcount=2, is_ref=1)=100
(refcount = 2)
PHP & (is_ref = 1)

33. $a
<?php
$a = 100;
$b = &$a;
$a++;
xdebug_debug_zval('a');
xdebug_debug_zval('b');
//==> a: (refcount=2, is_ref=1)=101
//==> b: (refcount=2, is_ref=1)=101
$a $b
PHP &

34. C

35. C

36. C …… PHP &

37. PHP
<?php
$a = 100;
$b = &$a;
$c = $a;
xdebug_debug_zval('a');
xdebug_debug_zval('b');
xdebug_debug_zval('c');
//==> a: (refcount=2, is_ref=1)=100
//==> b: (refcount=2, is_ref=1)=100
//==> c: (refcount=1, is_ref=0)=100
$c = $a
$a $b
$a $c (& )
is_ref
is_ref=1 is_ref=0

38. C ? ?

39. PHP
PHP : 1885
: 1753
: 132

40. PHP

41. <?php
calculareRankingScores($works, $users);
...
function calculareRankingScores(&$works, &$users)
{
for ($i = 0; $i < count($works);) {
...
count($array) O(1)
count($array_passed_by_reference) O(n)
calculareRankingScores() O(n^2)
(※ )

42. : PHP
<?php
$a = 100;
$b = &$a;
unset($b);
xdebug_debug_zval('a');
xdebug_debug_zval('b');
//==> a: (refcount=1, is_ref=0)=100
//==> b: no such symbol
refcount 1 is_ref 0
PHP & 1
copy-on-write is_ref = 0

43. PHP ……
PHP5
PHP7