php : How to check a field have blank/empty/NULL value?

I want to display an error when a variable have a BLANK value or EMPTY or NULL value. for example variable is shown below:

 $mo = strtotime($_POST['MondayOpen']);

and

var_dump($_POST['MondayOpen']) returns string(0) "".

Now I go with below approach

1. First want to find which type of variable $mo is ?(string or integer or other)

2. Which function is better to find that $mo having no value.

I conduct a test with $mo开发者_运维知识库 and got these results

is_int($mo);//--Return nothing
is_string($mo); //--Return bool(false) 
var_dump($mo);  //--Return bool(true)                   
var_dump(empty($mo));//--Return bool(true) 
var_dump($mo==NULL);//--Return bool(true) 
var_dump($mo=='');//--Return nothing

Please suggest an optimum and right approach to check the variable integrity

---

var_dump outputs variables for debugging purposes, it is not used to check the value in a normal code. PHP is loosely typed, most of the time it does not matter if your variable is a string or an int although you can cast it if you need to make sure it is one, or use the is_ functions to check.

To test if something is empty:

if ( empty( $mo ) ) {
  // error
}

empty() returns true if a variable is 0, null, false or an empty string.

---

doing strtotime will return false if it cannot convert to a time stamp.

$mo = strtotime($_POST['MondayOpen']);
if ($mo !== false)
{
//valid date was passed in  and $mo is type int
}
else
{
//invalid date let the user know
}

---

PHP offers a function isset to check if a variable is not NULL and empty to check if a variable is empty.

To return the type, you can use the PHP function gettype

if (!isset($mo) || is_empty($mo)) {
 // $mo is either NULL or empty.
 // display error message
 }

---

You can check its type using:

gettype($mo);

but null and empty are different things, you can check with these functions:

if (empty($mo))
{
  // it is empty
}

if (is_null($mo))
{
  // it is null
}

Another way to check if variable has been set is to use the isset construct.

if (isset($mo))
{
  // variable has been set
}