| Re: empty - not empty() [message #176310 is a reply to message #176304] |
Tue, 20 December 2011 13:14   |
bill
Messages: 310
Registered: October 2010
Karma:
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Senior Member |
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On 12/19/2011 8:14 PM, Chuck Anderson wrote:
> J.O. Aho wrote:
>> bill wrote:
>>> searching the manual gives lots of hits, none of which appear
>>> relevant (at
>>> least by the title).
>>>
>>> I had the following code in a scheduling class:
>>>
>>> if ($ptNum == "empty") {
>>> $ptNum = 0;
>>> $status= "e";
>>> }
>>>
>>> I pass the string "empty" to the function as a patient number
>>> if we are
>>> creating an empty appointment slot.
>>>
>>> now, this fails because with a patient number of 0 the if
>>> returns true.
>>>
>>> I am aware of the function empty() that would work like that,
>>> but do not
>>> understand why the compare fails with the constant, "empty."
>>
>> I assume you are comparing 0 and not the string "0", this makes
>> you are comparing integer with string, there ain't any type
>> conversion done.
>
> Actually, it is because there *is* an automatic type conversion
> done when comparing a string to an int.
>
> "If you compare a number with a string or the comparison involves
> numerical strings, then each string is converted to a number and
> the comparison performed numerically."
>
> ... http://us.php.net/manual/en/language.operators.comparison.php
>
>> The zero is always equal to a string,
>
> Not true.
> "If the string starts with valid numeric data, this will be the
> value used. Otherwise, the value will be 0 (zero)."
>
> ....
> http://us.php.net/manual/en/language.types.string.php#language.types.string .conversion
>
>
>> there is a slightly more information at
>>
>> http://php.net/manual/en/language.operators.comparison.php
>
> You might want to take a closer look at that page.
>
> The literal string "empty" does not begin with a numerical
> character so it will be converted to the integer 0.
Thank you, that makes sense.
>
>>> the regular compare is true with the numeric value of zero.
>> I fixed the function by making it a strict compare, but would
>> like to know why
>>
>> I would say it's not the right way to compare, use strcmp,
>> is_numeric and so on, to make a proper compare instead of using
>> the comparison operator.
>>
>
> I think you have that backwards. The identical (strict)
> comparison is far more efficient than a function call and this
> it's intended usage. "===" compares value and type (so no type
> conversion). Hence the string "empty" does not equal (===) the
> integer 0.
>
Glad to know that I stumbled onto the right way to do it.
Your comments are much appreciated and enlightening.
bill
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