Is the PHP variable present?

In PHP, you can use the isset() and empty() functions to check if a variable exists.

The isset() function is used to check if a variable has been declared and is not NULL. It returns true if the variable exists and is not NULL, otherwise it returns false.

The empty() function is used to check if a variable is empty. It returns true if the variable is false, 0, an empty string, an empty array, NULL, or undefined; otherwise, it returns false.

Here are some examples:

$var = "Hello World";

// 使用 isset() 检查变量是否存在
if (isset($var)) {
    echo "变量存在";
} else {
    echo "变量不存在";
}

// 使用 empty() 检查变量是否存在且为空
if (empty($var)) {
    echo "变量为空";
} else {
    echo "变量不为空";
}

In the example above, the variable $var exists and is not empty, so it will output “variable exists” and “variable is not empty”.