This is a bit of a tricky one to explain but I've never come across this before so I've got no idea how to properly approach it. I'm writing a web app that when a form is submitted, it takes two values, the current value and the submitted value.
When the form is submitted, it checks that the new value is not the same as the current value. If that is true, then go through the rest of the process. This is so I'm not updating the database with values that already exist in there.
Problem is I have an assigned to select box. One of the options is unassigned which has a value of 0. But in the following if statement, zero is not treated as a proper value and thus fails the check.
( $newtaskassignee != $taskassignid ) { ... do something ... }
So when $newtaskassignee is 0, the following if statement should be true and carry on what is inside the immediate curly brackets.
However in this statement, zero is ignored and doesn't pass the check. How can I change this so it accepts numbers from 1 to 9 including 0. This checks user IDs so they could be anything so I can't select a range as it increments by 1 per user obviously.
( $newtaskassignee !== $taskassignid )
The extra = will do an exact match and won't take 0 as false but 0.
As PHP has not strong types, there are two sets of equality operators.
one set that focus on value only : == and !=
and
one that focus on value AND type : === and !==
When you compare '' and 0, == will return true as, for PHP, these are same values.
So you may use === comparison operator to ensure that both operands are same value AND type.
Have a look on http://php.net/manual/en/language.operators.comparison.php, and particularly the difference between "equal" and "identical".
Hope this help
Related
I am trying to run an if statment then checks if a cell in database holds a certain value then it sets a variable, if it does not contain that value then it sets a different value
I have tried the following code
case "Chemistry":
$type_tarin_text = ' Exp in ';
if($user_playerdata_tab['profile_type']='Drug Runner') {
$treining_value =$sp_value*11;
} else {
$treining_value =$sp_value*10;
}
$this->AddSubValueByUserID($player_id,'PlayerData','CHEMISTRY_EXP',$treining_value);
break;
It is currently setting the $treining_value as $sp_value*11 regardless of wether profile_type is 'Drug Runner' or not.
Please use == or strict === since you're expecting a string.
You're now assigning a variable which is likely not what you are trying to do.
As others have helpfully pointed out, the issue is here:
$user_playerdata_tab['profile_type']='Drug Runner'
The single = means assignment. What you were intending to do was to test whether the two were equal.
That means using == - or, to be more strict, use === (make that your go-to equality check in the future - you'll thank us later)
Your other assignments are fine, though I would recommend a single space both sides of your = signs for readability
I have some of radio buttons and checkboxes elements in my HTML form which holds 0 as value. typically i would check for the required values using two functions isset() or !empty() while isset() works quite well without hindrance but this is not the case with empty() as logically 0 represents boolean and hence empty(0) returns true. which is kind of bug when you evaluates integer 0 using empty(). i would like to know the workaround so that it evaluates integer empty(0) as false. one solution i could think of was using strlen($variable) >= 1 , is there any better way or it is fine using strlen()?
thank you
You can check if a variable is exactly a value with three equals: ===
if( $variable === 0 ) {
will only be true if the variable is actually 0.
Use triple equal $variable===0
I noticed this weird evaluation yesterday after searching for a few hours in my code for an error. i am passing scores into php, sometimes the score=0 which causes an issue.
send php ?blah=blah&score=0
if(!empty($_REQUEST['score']){
//do database update stuff
}else{
// show entire webpage
}
It works great unless the score=0 the if() will evaluate to false and return the entire webpage to my ajax handler and error. I have temporarily changed !empty to isset but this will cause problems in the future because isset evaluates to true even if the score key is in the url string without a value.
ex: (?blah=blah&score=&something=else)
my question is: what is the best way to recode this to work correctly now and in the future?
edit: there are a few working answers here, i appreciate everyones time. it was difficult to choose an answer
As the manual says, a variable is considered empty() if it has an empty or zero value.
So it will treat your variable wrongly as empty even though 0 is a perfectly acceptable value in your case.
If you need score to be a number, you could use isset() in combination with a is_numeric() check instead:
if((isset($_REQUEST['score']) and (is_numeric($_REQUEST['score'])){
Check out the manual page to see the kinds of values is_numeric() accepts. If score is always an integer, you can also use is_int((int)$_REQUEST['score']) but that will convert invalid input values to 0.
Additionally, as #sightofnick says, it's better to use explicit $_GET or $_POST instead of $_REQUEST.
Re your update:
In that case I would
Do check whether the variable is "0" (string "zero")
If it is "0", make it 0 (integer "zero")
If it is not 0, convert it to an integer (int)$_REQUEST["score"])
If the conversion resulted in 0, it was invalid input - exit
You have a valid integer variable.
empty() will return false if a value is zero. Use isset() or array_key_exists() instead, if you want to check if a variable in an array is set:
if (array_key_exists('score', $_REQUEST)) {...}
Try doing
if (isset($_REQUEST['score']) && ($_REQUEST['score'] !== '')) {
...
}
The isset will handle the presence/absence of the query parameter, and the strict string (!==) comparison will handle the case where the 'score' query is present but has no value. PHP treats all data coming from _GET/_POST/_REQUEST as strings, so this test is 100% reliable.
if(isset($_REQUEST['score']) && $_REQUEST['score'] != ''){
//do database update stuff
}else{
// show entire webpage
}
You may be able to solve that with
if (isset($_REQUEST['score']) && is_numeric($_REQUEST['score'])) {}
That of course if scrore can only contain numeric value
I am new to the concept of empty and null. Whilst I have endeavoured to understand the difference between them, I am more confused. I came across an article at http://www.tutorialarena.com/blog/php-isset-vs-empty.php however I still don't see when you would use isset and empty when validating forms. Seeing that I don't grasp the difference, I don't want to be using the incorrect functions as well as not be able to use the functions in other areas. Can someone give examples that will help me understand? I am very new to coding so would appreciate if someone could give me real world examples and at the same time keep it simply enough for noob to follow.
A variable is NULL if it has no value, and points to nowhere in memory.
empty() is more a literal meaning of empty, e.g. the string "" is empty, but is not NULL.
The following things are considered to
be empty:
"" (an empty string)
0 (0 as an integer)
0.0 (0 as a float)
"0" (0 as a string)
NULL
FALSE
array() (an empty array)
var $var; (a variable declared, but without a value in a class)
Source.
Example
$a is NULL.
$a = '' is empty, but not NULL.
Update
If $a='' is empty but not NULL, when do I use the empty() function and when do I use the isset() function.
isset() will return FALSE is the variable is pointing to NULL.
Use empty() when you understand what is empty (look at the list above).
Also when you say it points nowhere in memory, what does that mean exactly?
It means that $str = '' will be in memory as a string with length of 0.
If it were $str = NULL, it would not occupy any memory.
Null is a placeholder that generally means "no data about this is available".
The use of null for this is just a convention, but a rather widespread one, to the point where some programming languages support the convention directly. The reason this convention exists has IMHO historically to do with "pointers";
many times a procedure will be defined to return a pointer to an answer, and will return what is traditionally called a Null pointer if it could not produce an answer for some reason.
Empty means (if this is a set) that it has no members. That's an explicit answer, and it is very different than "no data about this is available".
In the PHP world, apparantly uninitialized variables have the Null value, and isset on such a variable returns FALSE.
For arrays and strings, PHP follows the convention that "empty" means "has no members" although arrays and strings are not technically sets.
PHP apparantly has this funny idea that 0 and 0.0 are also "empty", by PHP design. That's abusive of the concept of "empty" IMHO: Individual numbers are not sets, so 0 can't reasonably by "empty". THis just leads to obscure programming because it violates the principle of least surprise. I'm sure the PHP designers would are that "zero is the empty number" as some kind of vague analogy; but the if analogy is vague, why bother with it? But then PHP is full of silly ideas.
The table below is an easy reference for what these functions will return for different values. The blank spaces means the function returns bool(false).
refer this link for more https://www.virendrachandak.com/techtalk/php-isset-vs-empty-vs-is_null/
NULL is a special value which explicitly states that the variable has not been set to any value yet. Be careful with using the empty() function as you can't just determine that a variable is exactly NULL using it. For example the empty() function will return true if an int is set to 0. If you need to make sure a variable is exactly NULL use if($variable == NULL).
For more info on empty() see http://php.net/manual/en/function.empty.php
There are some good answers here, which I won't repeat. In the case of validating forms, though, when a form is submitted, the value of each form input element is sent to the server in the $_POST variable. You can check for the existence of a particular input by using isset().
isset($_POST['username'])
If this returns true, then this request to the server was the result of posting a form containing an input element named "username". Now that we know that we have a value for that form element, we can see if it has a valid value. empty() will tell us whether the user actually entered any data in the field, or whether they left it empty.
empty($_POST['username'])
If that returns true then the form submitted to the server had a field named "username" but the user didn't enter anything into before submitting the form.
Been awhile since i used PHP but if other languages are anything to go by empty will indicate an existing object/map/array that has no contents while null would indicate a variable that has no meaning/definition at all (uninitialised).
In database SQL, NULL means "no value".
The empty() is a nice fast way to see if the variable holds any useful info... that is for strings empty() returns true for a string of "" as well as a null string.
So you can write something like this:
if (! empty($name)) echo $name;
More info see here: PHP: empty()
isset() returns true if both these conditions are met:
The variable has been defined and has not yet been unset.
The variable has a non-null value in it.
A variable is automatically defined when it gets set to something (including null). This has a direct implication in arrays.
$a=array();
$a['randomKey']=true;
$a['nullKey']=null;
var_dump(isset($a['randomKey'])); // true
var_dump(isset($a['nullKey'])); // true, the key has been set, set to null!
var_dump(isset($a['unsetKey'])); // false !
unset($a['randomKey']);
var_dump(isset($a['randomKey'])); // false ! it's been unset!
From above, you can check if various $_POST fields have been set. For example, a page that has been posted to, stands to reason, has the submit button name in the $_POST field.
empty() on the other hand, tests if the variable holds a non zero value. This means that values that (int) cast to 0, return false too. You can use this to see if a specific $_POST field has data in it.
This concept can be better understood from mathematics. Have you ever tried dividing a number (not zero) by 0 using a calculator e.g 7/0? You will get a result that looks like something this: undefined, not a number, null etc. This means that the operation is impossible, for some reasons (let's leave those reasons to be discussed another day).
Now, perform this: 0/7. You will get the output, 0. This means that the operation is possible and can be executed, but you the answer is just 0 because nothing is left after the division. There is a valid output and that output is zero.
In the first example, not only was the output invalid, the operation was not possible to execute. This is akin to null. The second example is akin to empty.
I was studying some code I found on the web recently, and came across this php syntax:
<?php $framecharset && $frame['charset'] = $framecharset; ?>
Can someone explain what is going on in this line of code?
What variable(s) are being assigned what value(s), and what is the purpose of the && operator, in that location of the statement?
Thanks!
Pat
Ah, I just wrote a blog post about this idiom in javascript:
http://www.mcphersonindustries.com/
Basically it's testing to see that $framecharset exists, and then tries to assign it to $frame['charset'] if it is non-null.
The way it works is that interpreters are lazy. Both sides of an && statement need to be true to continue. When it encounters a false value followed by &&, it stops. It doesn't continue evaluating (so in this case the assignment won't occur if $framecharset is false or null).
Some people will even put the more "expensive" half of a boolean expression after the &&, so that if the first condition isn't true, then the expensive bit won't ever be processed. It's arguable how much this actually might save, but it uses the same principle.
&& in PHP is short-circuited, which means the RHS will not be evaluated if the LHS evaluates to be false, because the result will always be false.
Your code:
$framecharset && $frame['charset'] = $framecharset;
is equivalent to :
if($framecharset) {
$frame['charset'] = $framecharset;
}
Which assigns the value of $framecharset as value to the array key charset only if the value evaluates to be true and in PHP
All strings are true except for two: a string containing nothing at all and a string containing only the character 0