Use of the middle-key in the foreach loop in php

The code is as follows: {code...} the final output result is as follows: {code...} question: why does the Get address character appear before the last key value? The code is as follows:

$a = [1, 2, 3];foreach($a as $key => &$value) {    $value = 5;}var_dump($a);

The output result is as follows:

array(3) { [0]=> int(5) [1]=> int(5) [2]=> &int(5) }

Q: Why does the Get address character appear before the last key value?

Reply content:

The code is as follows:

$a = [1, 2, 3];foreach($a as $key => &$value) {    $value = 5;}var_dump($a);

The output result is as follows:

array(3) { [0]=> int(5) [1]=> int(5) [2]=> &int(5) }

Q: Why does the Get address character appear before the last key value?

The & in this var_dump indicates that you can use another variable to change its value.
For example

$b = &$a[0];var_dump($a);

The & symbol appears in the first key value when printing, indicating that you can use other variables ($ B) to change its value.

Let's take a look&.

$b = $c = 1;$a = &$b;$a = 2;echo "b=$b,c=$c\n";$a = &$c;$a = 100;$a = 200;echo "b=$b,c=$c\n";unset($a);$a = 500;echo "b=$b,c=$c\n";

After $ a is specified as a reference of $ B, changing $ a is to change the value of $ B unless it is specified as another reference or unset ($.

The same is true for your foreach. you split the loop in one step, just like this:

$value = &$a[0];$value = 5;$value = &$a[1];$value = 5;$value = &$a[2];$value = 5;

When the loop is run to the end, $ value is a reference of $ a [2], so it is equivalent to this form:

$a[0] = 5;$a[1] = 5;$value = &$a[2];$a[2] = 5;var_dump($a);

It is not difficult to understand why var_dump prints an & symbol on the last key value.

Generally, this will not cause any major problems, but due to the scope of foreach, $ value can still be used after the loop exits, so some incredible bugs may occur.

For example

$a = [1, 2, 3];foreach($a as $key => &$value) {    $value = $value+5;}var_dump($a); // [6,7,8]foreach($a as $value){}var_dump($a); // [6,7,7]

After adding an empty foreach, $ a becomes unreasonable. this bug is incredible, the reason is that the $ value in the blank foreach is the reference of the & a [2] at the top.

The null foreach is equivalent to the following:

$value = &$a[2];$value = $a[0];$value = $a[1];$value = $a[2];

Note that because $ value is a reference of $ a [2], the above rewrite is as follows:

$a[2] = $a[0];$a[2] = $a[1];$a[2] = $a[2];

The empty foreach keeps changing $ a [2], and because $ a [2] has become the value of $ a [1, therefore, $ a [2] = $ a [2]; has no effect. The value is still $ a [1].

This incredible bug is caused by the scope of the $ value variable, so either change the name or give $ value to unset first.

$ A = [1, 2, 3]; foreach ($ a as $ key => & $ value) {$ value = $ value + 5;} var_dump ($ ); // either unsetunset ($ value); // do not use the $ value with the same name in foreach; change it to $ value2222foreach ($ a as $ value2222) {} var_dump ($ );

First, I want to say that this isVeryOkay. I believe that the subject does not clearly distinguish between reference and non-reference.
I did two tests first:

$a = [1, 2, 3];foreach($a as $key => &$value) {    $value = 5;}foreach($a as $key => $value) {    $value = 6;}var_dump($a);

Guess what the output is?

array(3) {  [0]=>  int(5)  [1]=>  int(5)  [2]=>  &int(6)}

Another test is:

$a = [1, 2, 3];foreach($a as $key => &$value) {    $value = 5;}foreach($a as $key => $value2) {    $value2 = 6;}var_dump($a);

This output looks much more normal:

array(3) {  [0]=>  int(5)  [1]=>  int(5)  [2]=>  &int(5)}

Therefore, this problem should be a pitfall of php global variables.