Variables in the PHP foreach Loop

A strange phenomenon occurred when using foreach, where the last value of an array variable was somehow modified, and the PHP manual foreach description found

Warning

The $value reference of the last element of the array remains after the Foreach loop. It is recommended to use unset () to destroy it.

There is such a warning. Use the Unset method or use a different variable name.

For example

$a =[1,2];foreach ($a as $key = = $value) {    $a [$key]= $value +1;} echo $value;//Output 2

If a pointer is used in $ A, the value of the variable with the same name will be affected, with the following result:

$a =[1,2]; $b =[3,4];foreach ($a as $key =>& $value) {    $a [$key]= $value +1;} Print_r ($a); foreach ($b as $value) {    $value + +;} Print_r ($a);p rint_r ($b); the output is as follows array (    [0] = 2    [1] = 3) array (    [0] = 2    [1] + 5) Array (    [ 0] = 3    [1] = 4)

If you use pointers or use unset, they are unaffected

$a =[1,2]; $b =[3,4];foreach ($a as $key =>& $value) {    $a [$key]= $value +1;} Print_r ($a); foreach ($b as & $value) {    $value + +;} Print_r ($a);p rint_r ($b); Enter the following array (    [0] = 2    [1] = 3) 3Array (    [0] = 2    [1] = 3) Array ( C14/>[0] + 4    [1] = 5)

Using unset

$a =[1,2]; $b =[3,4];foreach ($a as $key =>& $value) {    $a [$key]= $value +1;} Print_r ($a), unset ($key, $value), foreach ($b as $key = $value) {    $b [$key]= $value +1;} Print_r ($a);p rint_r ($b); the output is as follows array (    [0] = 2    [1] = 3) array (    [0] = 2    [1] + 3) array (    [ 0] = 4    [1] = 5)

Variables in the PHP foreach Loop