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Php – Check if argument is given in a function parameter

This question have a similar question here and here, too. I could have posted this as a comment but I don’t have the privilege yet so I posted this. I have also found similar question with no answer that satisfy my requirements. I will do the codes do the further talking.

I c/c++ you can do like this:

void CallMe(int *p = NULL)
{
    if ( p!= NULL )
        *p = 0;
}

CallMe(); // Calling the function without arguments the function will do nothing. But...

int n;
CallMe(&n);
// Here, you are passing a pointer to your n that will be filled by the CallMe function.
For c/c++ programmer, you know what to expect on those two calls.

Now, I want to do it in PHP. And when I do my searching, the following are most popular methods that are suggested in the search result: isset, is_null and empty. I did my trial-and-error but nothing works like that c/c++ sample.

function CallMe(&$p=null)
{
    if ($p==null)
        return;

    if(!isset($p))
        return;

    if (is_null($p))
        return;

    if (empty($p))
        return;
    $p = time();
    return 'Argument was set to ' . $p;
}

CallMe();

On the first call where no argument is supplied, all argument evaluations will result to true and the function will do nothing. Let’s try with an argument.

$a = 1;
CallMe($a);

Of source, the function will now make some sense out of that $a variable. But…

$a = null;
CallMe($a);

In this last call, the function will behave as if no argument is given.

Now, what I want to achieve is the function to be able to check (like the c/c++ sample) if an argument was supplied. Or, is there a way we could pass a pointer to a variable in PHP?

Tags:

2

Answers


  1. 0

    There is an old function you may call to check the number of function arguments that is actually supplied by user: func_num_args()

    function CallMe(&$p=null)
{
    if (func_num_args() === 0)
    {
        // no argument supplied. do nothing.
        return;
    }
    $p = time();
    return 'Argument was set to ' . $p;
}

echo "Try supplying no argument:n";
echo "---n";
var_dump(CallMe());
echo "n";

echo "Try supplying a variable with a value of null:n";
echo "---n";
$a = null;
var_dump($a);
var_dump(CallMe($a));
var_dump($a);

    Output:

    Try supplying no argument:
---
NULL

Try supplying a variable with a value of null:
---
NULL
string(30) "Argument was set to 1715217065"
int(1715217065)
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  2. 0

    The main difference is C / C++ has a distinct pointer type, while PHP does not. From a function perspective, there is no way to distinguish if $p is:

    1. NULL; or
    2. a variable (e.g. $a) with a NULL value

    There used to be run time pass-by-reference in PHP, but it was removed back in PHP 5. Which means the lack of reference / pointer type is probably a design choice of the language. And it’s unlikely to change in the foreseeable future.

    If you have multiple optional value, the closest thing I can think of is to use a value holder object instead of raw variable.

    class Inter
{
        private int $i;

        public function set($val)
        {
                $this->i = $val;
                return $this;
        }

        public function get(): int
        {
                if (!isset($this->i)) {
                        throw new Exception('No value is set');
                }
                return $this->i;
        }
}

function CallMe(?Inter $p=null, ?Inter $q=null) {
        if ($p !== null) {
                $p->set(time());
        }
        if ($q !== null) {
                $q->set(time());
        }
}

$a = new Inter();
$b = new Inter();
$b->set(1);
$c = new Inter();
CallMe(p: $a);
CallMe(q: $b);

var_dump($a->get());
var_dump($b->get());
var_dump($c->get());

    In PHP, object instances are ALWAYS passed by reference. Hence there is no need to explicitly add a & to it.

    Output:

    int(1715219664)
int(1715219664)
PHP Fatal error:  Uncaught Exception: No value is set in /home/foobar/test.php:16
Stack trace:
#0 /home/foobar/test.php(40): Inter->get()
#1 {main}
  thrown in /home/foobar/test.php on line 16

    This is not exactly what you asked for, but this is the closest I can think of.

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