How to use foreach to modify an array in php

php foreach method to modify the array: first create a PHP sample file; then modify the specified array through the foreach statement "foreach($array as $k => $v){$v = 1;}" The value is enough.

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The problem of using foreach to change the value of an array in PHP

Turn to the foreach page of the PHP documentation and it says:

"The foreach syntax structure provides a simple way to traverse the array. foreach can only be applied to arrays and objects. If you try to apply it to other data types Variables, or uninitialized variables will issue an error message. There are two syntaxes:

foreach (array_expression as $value)
    statement
foreach (array_expression as $key => $value)
    statement

The first format iterates over the given array_expression array. In each loop, the value of the current cell is assigned to $value and The pointer inside the array moves forward one step (so the next element will be obtained in the next loop).

The second format does the same thing, except that the key name of the current element will also be updated each loop is assigned to the variable $key."

Then "The first format traverses the given array_expression array. In each loop, the value of the current unit is assigned to $value and the array The internal pointer moves forward one step (so the next unit in the loop will be obtained)." What does this mean? This means that using foreach to traverse an array operates on a copy of the specified array, not the array itself. Just like having a clone of you, no matter how others punch or kick the clone of you, it will have no effect on you.

For example:

foreach($array as $k => $v){
　　$v = 1;
}

Such a modification method does not modify $array itself, but modifies an array it copies. Although it is the same, it is not $array. Therefore, it has no impact on $array.

So what to do? To do this:

foreach($array as $k => $v){
　　$array[$k] = 1;
}

Although $k and $v are also copied, the value of the copied $k is still the same as the value of $k in the original array, so this will succeed.

There is also a more advanced method: you can easily modify the elements of the array by adding & before $v. This method assigns by reference rather than copying a value. For example:

foreach($array as &$v){
　　$v = 1;
}
unset($v); // 最后取消掉引用

This will be successful.

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