Zero and NULL

[Paul Lautman]

I have the following switch statement:

switch ($record->sub_page) {
case -1:
$this->page = 6;
$error_message = '<center>You appear to have already completed the
form.</center>';
break;
case 0:
$this->page = 5;
ff_query("UPDATE #__gateway_form_1 SET `sub_page`=-1 WHERE
userid=$my->id and `expiry_date` = '$expiry_date'");
break;
default:
do something else
}

The value of $record->sub_page can be NULL. If it is NULL, the case for 0
seems to fire. I really need the default action to happen when
$record->sub_page is NULL or a +ve value.

However if I do:

switch ($record->sub_page) {
case -1:
$this->page = 6;
break;
case NULL:
do something else;
break;
case 0:
$this->page = 5;
break;
default:
do something else;
}

then the switch manages to tell the difference between a NULL and a zero.

Is it correct that php treats NULL as 0?
Can anyone suggest a good fix?

TIA
Regards
Paul

[J.O. Aho]

Paul Lautman wrote:

I have the following switch statement:

switch ($record->sub_page) {
case -1:
$this->page = 6;
$error_message = '<center>You appear to have already completed the
form.</center>';
break;
case 0:
$this->page = 5;
ff_query("UPDATE #__gateway_form_1 SET `sub_page`=-1 WHERE
userid=$my->id and `expiry_date` = '$expiry_date'");
break;
default:
do something else
}

The value of $record->sub_page can be NULL. If it is NULL, the case for 0
seems to fire. I really need the default action to happen when
$record->sub_page is NULL or a +ve value.

However if I do:

switch ($record->sub_page) {
case -1:
$this->page = 6;
break;
case NULL:
do something else;
break;
case 0:
$this->page = 5;
break;
default:
do something else;
}

then the switch manages to tell the difference between a NULL and a zero.

Is it correct that php treats NULL as 0?
Can anyone suggest a good fix?

NULL and 0 are many times treated as false, so you do need to take care of
things and check NULL/0/false.

--

//Aho

[Paul Lautman]

J.O. Aho wrote:

Paul Lautman wrote:

>I have the following switch statement:

switch ($record->sub_page) {
case -1:
$this->page = 6;
$error_message = '<center>You appear to have already completed
the form.</center>';
break;
case 0:
$this->page = 5;
ff_query("UPDATE #__gateway_form_1 SET `sub_page`=-1 WHERE
userid=$my->id and `expiry_date` = '$expiry_date'");
break;
default:
do something else
}

The value of $record->sub_page can be NULL. If it is NULL, the case
for 0 seems to fire. I really need the default action to happen when
$record->sub_page is NULL or a +ve value.

However if I do:

switch ($record->sub_page) {
case -1:
$this->page = 6;
break;
case NULL:
do something else;
break;
case 0:
$this->page = 5;
break;
default:
do something else;
}

then the switch manages to tell the difference between a NULL and a
zero. Is it correct that php treats NULL as 0?
Can anyone suggest a good fix?

NULL and 0 are many times treated as false, so you do need to take
care of things and check NULL/0/false.

But I need the default action to happen if $record->sub_page is NULL.

If I test for NULL before testing for 0 then all is detected fine. However
if I test for NULL after testing for 0 then it fires the 0 action when it
sees NULL. I don't really want to copy the default actions to the NULL
actions too.

[Heiko Richler]

Paul Lautman wrote:

I have the following switch statement:

switch ($record->sub_page) {
case -1:
$this->page = 6;
$error_message = '<center>You appear to have already completed the
form.</center>';
break;
case 0:
$this->page = 5;
ff_query("UPDATE #__gateway_form_1 SET `sub_page`=-1 WHERE
userid=$my->id and `expiry_date` = '$expiry_date'");
break;
default:
do something else
}

The value of $record->sub_page can be NULL. If it is NULL, the case for 0
seems to fire. I really need the default action to happen when
$record->sub_page is NULL or a +ve value.

select in php uses == and 0 == null seams to be true

However if I do:

switch ($record->sub_page) {
case -1:
$this->page = 6;
break;
case NULL:
do something else;
break;
case 0:
$this->page = 5;
break;
default:
do something else;
}

then the switch manages to tell the difference between a NULL and a zero.

if sub_page is 0 it sets page=5 ?

Is it correct that php treats NULL as 0?

Yes, as == does.

Can anyone suggest a good fix?

Use if and ===:

if ($record->sub_page === 6) ...
elseif ($record->sub_page === 5) ...
elseif ($record->sub_page === 1) ...
elseif ($record->sub_page === 0) ...
elseif ($record->sub_page === null) ...
else ...

Heiko
--
http://portal.richler.de/ Namensportal zu Richler
http://www.richler.de/ Heiko Richler: Computer - Know How!
http://www.richler.info/ private Homepage

[Umberto Salsi]

"Paul Lautman" <pa**********@btinternet.comwrote:

Is it correct that php treats NULL as 0?

The switch() statement uses the weak comparison operator ==.
When the weak operator == is used the reply is yes: 0==NULL.

Can anyone suggest a good fix?

1. Avoid to mix different types in expressions: it's confusing and dangerous.
For example, ensure the expression inside the switch() be int: switch( (int)
(EXPR) ){ ... }. Avoid to use a string as selector because "09" == 9 ==
"0x9" ==... difficult to say what ever else can match.

2. Do not use the switch(), use if() instead with the strong comparison
operator === as in this example:

if(EXPR === 1){
}else if(EXPR === NULL){
}else{
}

Best regards,
___
/_|_\ Umberto Salsi
\/_\/ www.icosaedro.it

[Paul Lautman]

Heiko Richler wrote:

if sub_page is 0 it sets page=5 ?

Yep it sure does.

Thanks for the hint on the way that switch comares work.

Wierd thing is that, whilst it seems to treat NULL as 0, if I put a NULL
test in befor ethe 0 one, it does not detect 0 as NULL.

So it seems NULL = 0 but 0 != NULL.

[J.O. Aho]

Paul Lautman wrote:

J.O. Aho wrote:

>Paul Lautman wrote:

>>I have the following switch statement:

switch ($record->sub_page) {
case -1:
$this->page = 6;
$error_message = '<center>You appear to have already completed
the form.</center>';
break;
case 0:
$this->page = 5;
ff_query("UPDATE #__gateway_form_1 SET `sub_page`=-1 WHERE
userid=$my->id and `expiry_date` = '$expiry_date'");
break;
default:
do something else
}

The value of $record->sub_page can be NULL. If it is NULL, the case
for 0 seems to fire. I really need the default action to happen when
$record->sub_page is NULL or a +ve value.

However if I do:

switch ($record->sub_page) {
case -1:
$this->page = 6;
break;
case NULL:
do something else;
break;
case 0:
$this->page = 5;
break;
default:
do something else;
}

then the switch manages to tell the difference between a NULL and a
zero. Is it correct that php treats NULL as 0?
Can anyone suggest a good fix?

NULL and 0 are many times treated as false, so you do need to take
care of things and check NULL/0/false.

But I need the default action to happen if $record->sub_page is NULL.

If I test for NULL before testing for 0 then all is detected fine. However
if I test for NULL after testing for 0 then it fires the 0 action when it
sees NULL. I don't really want to copy the default actions to the NULL
actions too.

This should work, you set 0 as the next last option in the switch and default
as last (as it should), then checking for null in the case 0 should allow you
to distinguish it from NULL.

switch($something) {

case 0:
if(!is_null($something)) {
/* do what you need for 0 */
break;
}
/* No break for NULL we go automatically to the next one */
default:
break;
}

--

//Aho

[Paul Lautman]

J.O. Aho wrote:

Paul Lautman wrote:

>J.O. Aho wrote:

>>Paul Lautman wrote:
I have the following switch statement:

switch ($record->sub_page) {
case -1:
$this->page = 6;
$error_message = '<center>You appear to have already completed
the form.</center>';
break;
case 0:
$this->page = 5;
ff_query("UPDATE #__gateway_form_1 SET `sub_page`=-1 WHERE
userid=$my->id and `expiry_date` = '$expiry_date'");
break;
default:
do something else
}

The value of $record->sub_page can be NULL. If it is NULL, the case
for 0 seems to fire. I really need the default action to happen
when $record->sub_page is NULL or a +ve value.

However if I do:

switch ($record->sub_page) {
case -1:
$this->page = 6;
break;
case NULL:
do something else;
break;
case 0:
$this->page = 5;
break;
default:
do something else;
}

then the switch manages to tell the difference between a NULL and a
zero. Is it correct that php treats NULL as 0?
Can anyone suggest a good fix?
NULL and 0 are many times treated as false, so you do need to take
care of things and check NULL/0/false.

But I need the default action to happen if $record->sub_page is NULL.

If I test for NULL before testing for 0 then all is detected fine.
However if I test for NULL after testing for 0 then it fires the 0
action when it sees NULL. I don't really want to copy the default
actions to the NULL actions too.

This should work, you set 0 as the next last option in the switch and
default as last (as it should), then checking for null in the case 0
should allow you to distinguish it from NULL.

switch($something) {

case 0:
if(!is_null($something)) {
/* do what you need for 0 */
break;
}
/* No break for NULL we go automatically to the next one */
default:
break;
}

Hey, I like it! Thanks

[Paul Lautman]

David Gillen wrote:

Paul Lautman said:

>Heiko Richler wrote:

>>if sub_page is 0 it sets page=5 ?

Yep it sure does.

Thanks for the hint on the way that switch comares work.

Wierd thing is that, whilst it seems to treat NULL as 0, if I put a
NULL test in befor ethe 0 one, it does not detect 0 as NULL.

So it seems NULL = 0 but 0 != NULL.

Not if I run this block of code.
<?
if(0 != NULL)
{
echo "0 is NOT equal to NULL<br>\n";
}
else
{
echo "0 is equal to NULL<br>\n";
}

if(NULL == 0)
{
echo "NULL is equal to 0<br>\n";
}
else
{
echo "NULL is not equal to 0<br>\n";
}

>>

Result is
0 is equal to NULL
NULL is equal to 0

D.

But I wasn't running that code. I was using switch.

[Sanders Kaufman]

Paul Lautman wrote:

I have the following switch statement:

Is it correct that php treats NULL as 0?
Can anyone suggest a good fix?

Stuckle had a great little one-line if-then to deal with that.
He posted it for me a few days ago, but I didn't save it.
I was gonna axe him to repost it, and this is a good opportunity.

Would you post it again, Herr Stuckle?

[jussist]

Why don't we instead tweak the whole concept of magic numbers? And
don't use 0 there at all - but something else, 1&2, or.

static $STATE_ALREADY_COMPLETED = 1152; // Or whatever, was -1
static $STATE_COMPLETE_NOW = 1153; // Or whatever, was 0

switch($record->sub_page) {
case $STATE_ALREADY_COMPLETED:
$this->page = 6;
$error_message = '<center>You appear to have already completed the
form.</center>';
break;
case $STATE_COMPLETE_NOW:
$this->page = 5;
ff_query("UPDATE #__gateway_form_1 SET `sub_page`=-1 WHERE
userid=$my->id and `expiry_date` = '$expiry_date'");
break;
default:
do something else
}

This solution is totally independent of what is the meaning of '-1' or
'0'. If you need to add more states, with whatever meaning, would you
prefer doing:
case 3:
doSomething2();
case 4:
doAnotherFunkyThing();
case 5:
whatTheHeckDoesFiveMean();

or

case $STATE_DO_SOMETHING:
doSomething2();
case $STATE_GET_FUNKY:
doAnotherFunkyThing();
case $STATE_FURIOUS_FIVE:
...

[Michael Fesser]

..oO(ju*****@gmail.com)

>Why don't we instead tweak the whole concept of magic numbers? And
don't use 0 there at all - but something else, 1&2, or.

static $STATE_ALREADY_COMPLETED = 1152; // Or whatever, was -1
static $STATE_COMPLETE_NOW = 1153; // Or whatever, was 0

define('STATE_ALREADY_COMPLETED', 1152);
define('STATE_COMPLETE_NOW', 1153);

Micha

[jussist]

Michael Fesser wrote:

.oO(ju*****@gmail.com)

Why don't we instead tweak the whole concept of magic numbers? And
don't use 0 there at all - but something else, 1&2, or.

static $STATE_ALREADY_COMPLETED = 1152; // Or whatever, was -1
static $STATE_COMPLETE_NOW = 1153; // Or whatever, was 0

define('STATE_ALREADY_COMPLETED', 1152);
define('STATE_COMPLETE_NOW', 1153);

Yeah! Fesser lead the way! :-)
That's the way to do IT.

That my part is for classes, right? Been working mostly with java
-lately.

t.j

[Michael Fesser]

..oO(ju*****@gmail.com)

>That my part is for classes, right?

In classes you can use the 'const' keyword for defining class constants.

>Been working mostly with java

Yep. ;)

But, unlike in Java, in PHP variables and constants are two different
things.

Micha