Passing 0 to function with default value

Question

Im currently testing a simple PHP function.

I want to to return the currently value of a field if the function is called without any parameter passed or set a new value if a parameter is passed. Strange thing is: if I pass 0 (var_dump is showing correct value int(1) 0), the function goes into the if branch like i called the function without any value and i just don't get why.

function:

public function u_strasse($u_strasse = 'asdjfklhqwef'){
  if($u_strasse == 'asdjfklhqwef'){
    return $this->u_strasse;
  } else {
    // set new value here
  }
}

either u_strasse() or u_strasse(0) gets me in the if branch.

In the meanwhile I came up with an even better solution, I´m using the default value only PHP reports a warning when calling the function without a parameter and use func_num_args() to choose what to do. if func_num_args() === 0 -> return value, else set new value — Chris
– Chris, Commented Mar 25, 2013 at 10:55

Ynhockey · Accepted Answer · 2012-03-05 15:49:30Z

4

You should use null as the default value:

public function u_strasse($u_strasse = null)
{
    if ($u_strasse === null) { $u_strasse = 'asdjfklhqwef'; }

    // rest of function
}

answered Mar 5, 2012 at 15:49

Ynhockey

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1 Comment

Chris Over a year ago

Good solution, never tried it with null before so thanks for that. Still i don´t get why PHP is interpreting 0 as default value if it isn´t.

DaveyBoy · Accepted Answer · 2012-03-05 16:00:44Z

1

When comparing variables of different types (specifically strings and numbers), both values will be converted to a number. Therefore, your 'asdjfklhqwef' converts to 0 (number), the comparison is true.

http://www.php.net/manual/en/language.operators.comparison.php

answered Mar 5, 2012 at 16:00

DaveyBoy

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1 Comment

Chris Over a year ago

Thanks. Already had a look at this link but i kinda misslooked this. That was the answer i was looking for :)

a.tereschenkov · Accepted Answer · 2012-03-05 15:56:30Z

1

Use === instead of ==:

public function u_strasse($u_strasse = 'asdjfklhqwef'){
  if($u_strasse === 'asdjfklhqwef'){
    return $this->u_strasse;
  } else {
    // set new value here
  }
}

In case of == php tries to convert 'asdjfklhqwef' to number (because you pass $u_strasse as a number) and (int)'asdjfklhqwef' equals 0. To avoid this behavior you need to compare strictly (===)

Read more about difference in == and === here

answered Mar 5, 2012 at 15:56

a.tereschenkov

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Comments

Stewie · Accepted Answer · 2012-03-05 15:49:52Z

0

Pass '0' instead of 0. The former will be a string. You can cast it like this:

$myvar = 0;

u_strasse((string)$myvar);

answered Mar 5, 2012 at 15:49

Stewie

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2 Comments

Chris Over a year ago

I know I´m just curious why 0 is treated as default value. If I test with === it works

Marc B Over a year ago

PHP will type-convert for you automatically. since you pass in a 0 and that's on the left, the string will be converted to an int as well, and end up being '0' as well. If your string had (say) a '9' as its first character, you'd end up with 0 == 9 and go through the false path.

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