I found an example php assignment statement online which maybe resembles a tertary conditional condensed statement, but not quite. Does anyone have insight as to how to read this assignment statement?
$access = $access || $note->uid == $user->uid && user_access('note resource view own notes');
My first guess was "assign to access whatever is in access, or if empty, whether uid values are equal and'd with the return of user_access." But I get the feeling that is not correct, as it seems illogical.
First have a look at the Operator Precedence
== comes before && comes before || comes before =
Thus your statement is more clear with adding the following parentheses:
$access = (
$access
||
(
($note->uid == $user->uid)
&&
user_access('note')
)
);
assign to access whatever is in access, or if empty,
Not quite: assign to $access the value true* when $access already evaluates to true (true, 1, "some string" etc), or
whether uid values are equal and'd with the return of user_access
Correct
And otherwise assign false. After this statement $access is always either true or false, even when $access === 'yes' before.
Note*: || and && are boolean operators, only capable of 'returning' true or false
I had this exact type of statement in a library way back, and it's basically an elaborate (or maybe just badly-styled?) null-check. Because PHP uses short circuit evaluation, the right-hand side of the or-expression will not evaluate if the left hand one was null.
Related
I want to make a function for a "secure" php page that will check the token(the one passed by post and the one from the session). But I don't want to write two if statements like this:
function CheckToken(){
if(isset($_POST['token']) && isset($_SESSION['token']))
if($_POST['token']==$_SESSION['token']) return true;
return false;
}
Can I do something like this(?):
function CheckToken(){
if(isset($_POST['token']) && isset($_SESSION['token']) && $_POST['token']==$_SESSION['token']) return true;
return false;
}
Here's all about the order in which those functions are executed (when using the and operator).So if you're using the AND operand then if the first conditions is false don't evaluate the second. I remember that vb.net had a solution to this problem(evaluating only the first function-if it is false don't evaluate the second one). So, is it safe to put everything on a single line(like I did in the second example)?
PHP does the same thing as the usual if statement evaluation in other major languages, that is, check from left to right.
So if you have
if (cond1 && cond2 && cond3)
Scenario 1:
If cond1 is true, it will then execute cond2, and then cond3.
Sample: https://3v4l.org/Ap9SQ
Scenario 2:
If let's say cond2 is false, then cond3 will be ignored.
Sample: https://3v4l.org/u9P4O
Same goes to OR
if (cond1 || cond2 || cond3)
If cond1 is true, cond2 and cond3 will be skipped.
Sample: https://3v4l.org/ZAZcD
So since your function is just returning true or false, you can even simplify it to something like this:
function CheckToken() {
return isset($_POST['token']) &&
isset($_SESSION['token']) &&
$_POST['token'] == $_SESSION['token'];
}
Split lines for readability. Also checkout isset manual as you can pass in multiple variables for empty checking.
Yes, there really is no difference to changing the order like that. It is perfectly safe, because all it's doing is changing the look of the script while the execution is the EXACT same.
It would be best to do the second option.
hah, why does name show value 1?
['name' => ($profile->getNickname() || $profile->getName()),]
a => b || c
if b is empty use c isn't it?
p.s. I know I can do normal if else shorthand (ternary), but its long and unreadable, I don't like it.
In javascript this is a common thing to write, but PHP will cast to booleans.
This question will answer yours: Best way to give a variable a default value (simulate Perl ||, ||= )
$name = $profile->getNickname() ?: $profile->getName();
In PHP, the boolean operators || and && always produce a boolean value; the operands are coerced to boolean if necessary, and the original value discarded. This is different from, for example, JavaScript, where the operands are evaluated for "truthiness" but their original values retained.
The 1 you see is just because you echoed a boolean, which in turn coerces the true to a string 1.
PHP does have a shorthand operator for what you want, though: ?:
($profile->getNickname() || $profile->getName()) is just a condition which comes true (1) that's why its showing 1.
it should be as follows:
// if nick name is set and not empty then show it otherwise show name
[ 'name' => ((isset($profile->getNickname()) && ($profile->getNickname() != "")) ? $profile->getNickname() : $profile->getName())]
return the boolean value from function if isset(data)
$profile->getNickname() and
$profile->getName()
to decision a condition.
I am new to PHP and am currently constructing a do/while loop from a tutorial. I would understand if the whole condition was ($variable == true) or ($variable == false), however in the tutorial the while condition is simply while($variable). Could anyone explain this to me?
Here is the tutorial code.
<?php
$loopCond = false;
do {
echo "<p>The loop ran even though the loop condition is false.</p>";
} while ($loopCond);
echo "<p>Now the loop is done running.</p>";
?>
All such conditional statements, including while and if, are evaluating the given expression against true. If the expression results in true, the statement executes the action. If it results in false, it won't.
$var == true is an expression which compares $var to true. The result of this expression is either true or false. The important point to understand here is expressions. Expressions are things which return values. Try var_dump($var == true) or var_dump(4 > 6). It shows you that the expressions return a boolean value. Here:
if ($var == true)
first $var is compared to true, which yields either the value true or false, which is then evaluated by if whether it's true or false, which then prompts if to execute the following statement or not.
In other words: it's redundant.
if ($var)
This simply causes if to evaluate whether $var is true or false and then execute the following statement. The == true is essentially already "built in".
The following statements are all essentially equivalent:
if ($var)
if ($var == true)
if (($var == true) == true)
if ((($var == true)) == true) == true)
...
A boolean value true or false should not be used with a redundant $c == true as the result is the same as $c: true or false
$driving = true;
while ($driving) {
while ($driving == true) { // ugly
while (! $driving) { // while not driving.
while ($driving == false) { // ugly
$drinking = ! $driving;
if ($driving && $drinking) {
Hence also use adjectives for boolean variables.
A condition is met, if the value or statement in it is considered as true.
The code $variable == true is a statement that looks whether the value of the variable is true and if it is, yields true - Or false if it is not.
However, as this means, that $variable itself can only ultimately be true or false, you don't even need the statement, as its return value will also be one of those two.
Therefore $variable is exactly the same as $variable == true.
I hope this made it clear.
The semantic of while/do-while is
while(<boolean expression>) {
// do your stuff
}
A boolean expression is anything that evaluates to true or false. So, if $loopCount is true, then $loopCount == true is checked on every loop and evalutes to true. But you could also write $LoopCount as condition, since it also evaluates to true.
This is very handy for using other data types, e.g. integers.
$count = 0;
while ($count < 10) {
$count = $count +1;
}
Here $count < 10 is a boolean expression that evaluates to true as long as $count is not higher then 9.
A while loop runs as long as the condition is met, in other words, as long as the boolean expression you provide evaluates to true.
You can also just use a variable, e.g. $loopCount when that variable evaluates to a boolean or a constant (even the constant value true).
Like Padarom said: Therefore $variable is exactly the same as $variable == true.
In your case: The while-do loop determines if redo the loop-body after the first run. Means the loop-body is executed exactly one time regardless what value $variable has. After the first run, the while($variable) checks if the expression is true. If so, the loop-body is executed second time and so forth.
Check PHP reference for do-while loops here. PHP.net do-while reference
while ($loopCond) and while ($loopCond == true) is the same thing. It checks the "trueness" of whatever you put in the brackets.
If I ask a question "does sun set in the west ? " what would be your answer, definitely YES OR TRUE. Same as compiler always look for statement value. Take a look
$condition = true;
if($condition == true )
// above will return TRUE; in short $condition == true will replaced by true at runtime. But if we place true directly which is $condition value or can say we place $condition instead true thus statement become shorten and look like...
if($condition) {
}
This is the conditional statement:
$comments = get_value_of_comments_as_string();
if( !$comments == "on" ){...}
What is the purpose of the ! point before the $comments variable especially since $comments holds a string.
Edit: this conditional doesn't seem to be a typo as the original coder had like 5 of these conditional statements. all like this.
! is the logical negation operator (or not) so basically it changes truthy values to false and falsey values to true.
I'm sure the author's intentions was to be
!($comments == "on") // if comments == "on" return false
but what his is actually saying is
(!$comments) == "on") // if not comments == "on" ... this test will only succeed if comments is null or an empty string.
A much better way to express this is
$comments != "on"
This behavior is because ! has a higher precedence then == so it will evaluate before the ==.
Considering that:
The isset() construct returns TRUE if a variable is set and not NULL
The is_null() function throws a warning if the variable is not set
Is there a way to test whether a variable exists, no matter it's NULL or not, without using the # operator to suppress the notice?
EDIT
Together with your first replies, I've been thinking about this and I'm getting the conclusion that inspecting get_defined_vars() is the only way to distinguish between a variable set to NULL and an unset variable. PHP seems to make little distinctions:
<?php
$exists_and_is_null = NULL;
// All these are TRUE
#var_dump(is_null($exists_and_is_null));
#var_dump(is_null($does_not_exist));
#var_dump($exists_and_is_null===NULL);
#var_dump($does_not_exist===NULL);
#var_dump(gettype($exists_and_is_null)=='NULL');
#var_dump(gettype($does_not_exist)=='NULL');
?>
$result = array_key_exists('varname', get_defined_vars());
As you already found out, you cannot :
rely on isset, as it return false for a variable that's null.
use $not_exists===null, as it'll raise a notice.
But you could be able to use a combinaison of :
get_defined_vars to get the list of existing variables, including those which are null,
and array_key_exists to find out if an entry exists in that list.
For instance :
$exists_and_null = null;
$exists_and_not_null = 10;
$defined_vars = get_defined_vars();
// true
var_dump(array_key_exists('exists_and_null', $defined_vars)
&& $defined_vars['exists_and_null']===null);
// false
var_dump(array_key_exists('exists_and_not_null', $defined_vars)
&& $defined_vars['exists_and_not_null']===null);
// false
var_dump(array_key_exists('not_exists', $defined_vars)
&& $defined_vars['not_exists']===null);
A couple of notes :
In the first case, the variable exists => there is an entry in the list returned by get_defined_vars, so the second part of the condition is evaluated
and both parts of the condition are true
In the second case, the variable exists too, but is null
which means the first part of the condition is true, but the second one is false,
so the whole expression is false.
In the third case, the variable doesn't exist,
which means the first part of the condition is false,
and the second part of the condition is not evaluated -- which means it doesn't raise a notice.
But note this is probably not that a good idea, if you care about performances : isset is a language construct, and is fast -- while calling get_defined_vars is probably much slower ^^
I would argue here that any code requiring such a comparison would have gotten its semantics wrong; NULL is an unset value in a language that has no straightforward way of distinguishing between the two.
I used a self created function to check this easily, keep in mind it will fire off a PHP warning (I only monitor E_ERROR when I develop).
function isNullOrEmpty( $arg )
{
if ( !is_array( $arg ) )
{
$arg = array( $arg );
}
foreach ( $arg as $key => $value )
{
if( $value == null || trim($value) == "" )
{
return true;
}
}
return false;
}
if (isset($var) && (is_null($var)) {
print "\$var is null";
}
This should do the trick.