基本的赋值运算符是“=”。一开始可能会以为它是“等于”，其实不是的。它实际上意味着把右边表达式的值赋给左边的运算数。
赋值运算表达式的值也就是所赋的值。也就是说，“$a = 3”的值是 3。这样就可以做一些小技巧：
<?php
$a = ($b = 4) + 5; // $a 现在成了 9，而 $b 成了 4。
?>
对于数组 array，对有名字的键赋值是用“=>”运算符。此运算符的优先级和其它赋值运算符相同。
在基本赋值运算符之外，还有适合于所有二元算术，数组集合和字符串运算符的“组合运算符”，这样可以在一个表达式中使用它的值并把表达式的结果赋给它，例如：
<?php
$a = 3;
$a += 5; // sets $a to 8, as if we had said: $a = $a + 5;
$b = "Hello ";
$b .= "There!"; // sets $b to "Hello There!", just like $b = $b . "There!";
?>
注意赋值运算将原变量的值拷贝到新变量中（传值赋值），所以改变其中一个并不影响另一个。这也适合于在密集循环中拷贝一些值例如大数组。
在 PHP 中普通的传值赋值行为有个例外就是碰到对象 object 时，在 PHP 5 中是以引用赋值的，除非明确使用了 clone 关键字来拷贝。
PHP 支持引用赋值，使用“$var = &$othervar;”语法。引用赋值意味着两个变量指向了同一个数据，没有拷贝任何东西。
Example #1 引用赋值
<?php
$a = 3;
$b = &$a; // $b 是 $a 的引用
print "$a\n"; // 输出 3
print "$b\n"; // 输出 3
$a = 4; // 修改 $a
print "$a\n"; // 输出 4
print "$b\n"; // 也输出 4，因为 $b 是 $a 的引用，因此也被改变
?>
自 PHP 5 起，new
运算符自动返回一个引用，因此再对
new
的结果进行引用赋值在 PHP 5.3 以及以后版本中会发出一条
E_DEPRECATED 错误信息，在之前版本会发出一条
E_STRICT 错误信息。
例如以下代码将产生警告：
<?php
class C {}
/* The following line generates the following error message:
* Deprecated: Assigning the return value of new by reference is deprecated in...
*/
$o = &new C;
?>
有关引用更多信息参见本手册中引用的解释一章。
haubertj at alfredstate dot edu (2011-09-01 07:19:40)
[[ Editor's note: You are much better off using the foreach (array_expression as $key => $value) control structure in this case ]]
When using
<php
while ($var = current($array) {
#do stuff
next($aray)
?>
to process an array, if current($array) happens to be falsy but not === false it will still end the loop. In such a case strict typing must be used.
Like this:
<php
while (($var = current($array)) !== FALSE) {
#do stuff
next($aray)
?>
Of course if your array may contain actual FALSE values you will have to deal with those some other way.
Peter, Moscow (2011-02-11 01:44:54)
Using $text .= "additional text"; instead of $text = $text ."additional text"; can seriously enhance performance due to memory allocation efficiency.
I reduced execution time from 5 sec to .5 sec (10 times) by simply switching to the first pattern for a loop with 900 iterations over a string $text that reaches 800K by the end.
Hayley Watson (2008-02-05 17:54:11)
You could also take adam at gmail dot com's xor-assignment operator and use the fact that it's right-associative:
$a ^= $b ^= $a ^= $b;
Hayley Watson (2007-10-07 15:22:17)
bradlis7 at bradlis7 dot com's description is a bit confusing. Here it is rephrased.
<?php
$a = 'a';
$b = 'b';
$a .= $b .= "foo";
echo $a,"\n",$b;?>
outputs
abfoo
bfoo
Because the assignment operators are right-associative and evaluate to the result of the assignment
<?php
$a .= $b .= "foo";
?>
is equivalent to
<?php
$a .= ($b .= "foo");
?>
and therefore
<?php
$b .= "foo";
$a .= $b;
?>
adam at gmail dot com (2006-08-25 10:38:21)
or you could use the xor-assignment operator..
$a ^= $b;
$b ^= $a;
$a ^= $b;
bradlis7 at bradlis7 dot com (2005-08-15 08:13:01)
Note whenever you do this
<?php
$a .= $b .= "bla bla";
?>
it comes out to be the same as the following:
<?php
$a .= $b."bla bla";
$b .= "bla bla";
?>
So $a actually becomes $a and the final $b string. I'm sure it's the same with numerical assignments (+=, *=...).
straz at mac dot nospam dot com (2004-02-20 22:18:19)
This page really ought to have table of assignment operators,
namely,
See the Arithmetic Operators page (http://www.php.net/manual/en/language.operators.arithmetic.php)
Assignment Same as:
$a += $b $a = $a + $b Addition
$a -= $b $a = $a - $b Subtraction
$a *= $b $a = $a * $b Multiplication
$a /= $b $a = $a / $b Division
$a %= $b $a = $a % $b Modulus
See the String Operators page(http://www.php.net/manual/en/language.operators.string.php)
$a .= $b $a = $a . $b Concatenate
See the Bitwise Operators page (http://www.php.net/manual/en/language.operators.bitwise.php)
$a &= $b $a = $a & $b Bitwise And
$a |= $b $a = $a | $b Bitwise Or
$a ^= $b $a = $a ^ $b Bitwise Xor
$a <<= $b $a = $a << $b Left shift
$a >>= $b $a = $a >> $b Right shift