What is the method in PHP to check if a variable is empty?

In PHP, you can check if a variable is empty using the following methods:

1. Check if the object is empty.
2. is not filled
3. Return true if the given array or string is empty.
4. It is true.

$var = '';
if(empty($var)) {
    echo '变量为空';
} else {
    echo '变量不为空';
}

1. determine if a variable is set
2. Check if a variable is set or not.
3. Check if a variable is set and is not NULL
4. correct

$var = '';
if(isset($var)) {
    echo '变量已设置';
} else {
    echo '变量未设置';
}

1. Does it equal null?
2. checks if a variable is null

$var = null;
if(is_null($var)) {
    echo '变量为 null';
} else {
    echo '变量不为 null';
}

These methods can be selected based on specific needs.