Instructions on adding the ampersand when learning the foreach loop in PHP

The main content of this article is about the instructions for adding the & symbol in PHP's foreach loop. Interested friends can learn more.

Add the ampersand when foreach: Change the original array while traversing, that is, modify the data or add data.

$arr = ['a', 'b', 'c'];
foreach ($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

Usage & possible problems:

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

This is because the value of $value is not released after passing by assignment reference, so it will affect the use of the second foreach. You can use unset($value) to release variables.

$arr = ['a', 'b', 'c'];
foreach ($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"]

Related courses: PHP video tutorial

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