Questions about reference and pass-through during loop

Two loops are performed on an array. The value of the array element is changed by reference for the first time, and $ k, $ v, why does the value of the last element of the array change without reference? And the last element has not changed? {Code ...}

Two loops are performed on an array. The value of the array element is changed by reference for the first time, and $ k, $ v, why does the value of the last element of the array change without reference? And the last element has not changed?

   &$v) {    switch ($v) {        case '1':            $v = 'a';            break;        case '2':            $v = 'b';            break;        case '3':            $v = 'c';            break;        case '4':            $v = 'd';            break;        case '5':            $v = 'e';            break;                default:            # code...            break;    }}var_dump($v);var_dump($arr);foreach ($arr as $k => $v) {    var_dump($v);}var_dump($arr);

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Two loops are performed on an array. The value of the array element is changed by reference for the first time, and $ k, $ v, why does the value of the last element of the array change without reference? And the last element has not changed?

   &$v) {    switch ($v) {        case '1':            $v = 'a';            break;        case '2':            $v = 'b';            break;        case '3':            $v = 'c';            break;        case '4':            $v = 'd';            break;        case '5':            $v = 'e';            break;                default:            # code...            break;    }}var_dump($v);var_dump($arr);foreach ($arr as $k => $v) {    var_dump($v);}var_dump($arr);

$ Arr = array (1, 2, 3, 4, 5); foreach ($ arr as $ k = >&$ v) {switch ($ v) {case '1 ': $ v = 'a'; break; case '2': $ v = 'B'; break; case '3': $ v = 'C'; break; case '4': $ v = 'd'; break; case '5': $ v = 'e'; break; default: # code... break ;}} var_dump ($ v); var_dump ($ arr); unset ($ v); // when foreach uses a reference, the reference relationship is closed immediately after processing, or the following $ v =>$ vaforeach ($ arr as $ k =>$ v) {var_dump ($ v) ;} var_dump ($ arr );

$ V = e after the first cycle; // reference link here & $ arr ['E'];

The last step of the second loop will be & $ v = $ arr ['D']; then & $ arr ['E'] = & $ v = $ arr ['D'];

This is a classic pitfall for PHP reference.

Solution: Add one after the first foreach.unset($v);You can.

The principle is omitted. you can google/baidu on your own.