PHP学习之foreach循环时加&符号的说明

$arr = ['a', 'b', 'c']; foreach ($arr as $key => &$value) { $value = $value . '111'; } echo json_encode($arr); // ["a111","b111","c111"]，这里改变了原来数组的值

$arr = ['a', 'b', 'c']; foreach ($arr as $key => &$value) { $value = $value . '111'; } foreach ($arr as $key => $value) { $value = $value . '222'; } echo json_encode($arr); // ["a111","b111","b111222222"]

$arr = ['a', 'b', 'c']; foreach ($arr as $key => &$value) { $value = $value . '111'; } unset($value); // 释放$value的引用传递 foreach ($arr as $key => $value) { $value = $value . '222'; } echo json_encode($arr); // ["a111","b111","c111"]