I have noticed that PHP doesn't run the second or other parameters of 'if statement' if the first parameter true.
if($this->sessions->remove("registered_id") or $this->sessions->remove("user_id")){
echo "you have logged out";
}else {
echo "wth?";
}
This how I use the if. Also here is the remove function from sessions class.
public function remove($key){
if(isset($_SESSION[$key])){
unset($_SESSION[$key]);
return true;
}
else
{
return false;
}
}
The thing that I want to do is run both of this parameters.. I hope I can tell the problem..
You need to execute both functions, store their respective results, then test on these results.
$resultA = $this->sessions->remove("registered_id");
$resultB = $this->sessions->remove("user_id");
if ($resultA or $resultB)
{
…
It's by design that the second statement is not executed, because its result will be irrelevant.
If by other parameters you mean the second condition, then use an AND instead of OR
If by other parameters you mean the else, then use a separate if statement instead.
edit
If you're trying to execute both statements, use bitwise operators, check out this manual:
http://www.php.net/manual/en/language.operators.bitwise.php
Something like:
if(a | b){
}
That will execute both a and b, but still is an 'or' comparison.
That result is to be expected. This is what logical operators do.
You would need to use && or and to achieve what you seem to be looking for:
if ($this->sessions->remove("registered_id") && $this->sessions->remove("user_id")) {
Here is why:
The && or and keyword means that all evaluations must return true. So:
if ($a && $b) {
// $a and $b must both be true
// if $a is false, the value of $b is not even checked
}
The || or or keyword means that either evaluation must return true. So:
if ($a || $b) {
// Either $a or $b must be true
// If $a is false, the parser continues to see if $b might still be true
// If $a is true, $b is not evaluated, as our check is already satisfied
}
So in your case, if the $this->sessions->remove("registered_id") successfully did it's thing, the $this->sessions->remove("user_id") is never called, as our check is already satisfied with the outcome of the first call.
Related
I often encounter situations like this:
function stuff()
{
$feed_data = blablabla(...);
if ($feed_data && isset($feed_data['posts'][0]['title']))
return $feed_data['posts'][0]['title'];
return false;
}
As you can see, $feed_data['posts'][0]['title'] is returned, but it's first checked with isset() to make sure it actually exists, which is not guaranteed.
If I do not include the isset() check, it can log even uglier errors about how it doesn't exist. (When things go wrong.)
Now I'm wondering if there is some way to only have to have one instance of the reference sting $feed_data['posts'][0]['title'] in my code, yet also do the check.
This is the most obvious "solution" which I've naturally tested:
$a = $feed_data['posts'][0]['title'];
if ($feed_data && isset($a))
return $a;
However, this will log the error at the first line, because you cannot assign a variable which doesn't exist!
I don't see a way around this, and it's been bothering me for a long time. I hate having duplicate code snippets like that in my code.
It seems like there ought to be a better way.
You can use a null coalescing operator:
$a = $feed_data['posts'][0]['title'] ?? false;
It checks against having a null value, if it does, return false, else return the long variable :)
Note that this was introduced with PHP 7, you can read more here
If you're specifically looking for $feed_data['posts'][0]['title'] then you don't need to check for both this value and the "parent" $feed_data array. Simply check only for this value, as one can not exist without the other.
As mentioned by treyBake you can use the ?? operator (PHP 7+) to place the value in the if statement, when the checks the value as to if the if is executed.
Combining these two points gives:
if($a = $feed_data['posts'][0]['title'] ?? false){
// Do stuff wth $a
return $a;
}
Pre PHP 7:
c'mon, update your system ;-)
NOTE: The result $a needs to be hard checked against false so that falsey values such as 0 or empty strings are not erroneously skipped (If you DO want to skip these falsey things; use empty instead of isset).
if(
($a = isset($feed_data['posts'][0]['title']) ?
$feed_data['posts'][0]['title'] : false) !== false) {
//do stuff with $a
return $a;
}
I am new to PHP and am currently constructing a do/while loop from a tutorial. I would understand if the whole condition was ($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) {
}
The point is to validate, only when,
$this->data[$this->alias]['enabled']
It's equal to one. So, if $this->data[$this->alias]['enabled'] == 1, validate.
I was expecting that this peace of code, would do the job:
public function compareDates() {
if ($this->data[$this->alias]['enabled'] == 1) {
return $this->data[$this->alias]['firstPageEnterDate'] < $this->data[$this->alias]['firstPageLeaveDate'];
}
}
However it seems that that doesn't work as I expected. Instead, it gets always validated, regardless the value of $this->data[$this->alias]['enabled']
This code, however, seems to do the job just fine:
public function compareDates() {
if ($this->data[$this->alias]['enabled'] != 1) return true; // we don't want to check
return $this->data[$this->alias]['firstPageEnterDate'] < $this->data[$this->alias]['firstPageLeaveDate'];
}
What is, in your understanding, the meaning of "we don't want to check"?
Why: if ($this->data[$this->alias]['enabled'] == 1) is not enough?
Can anyone care to explain?
Update:
If I do:
public function compareDates()
{
if ($this->data[$this->alias]['enabled'] === "1") {
return $this->data[$this->alias]['firstPageEnterDate'] < $this->data[$this->alias]['firstPageLeaveDate'];
} else {
return true;
}
}
It works as well. My question is:
Why do I need to explicitly declare the return true?;
You're doing a simple comparison (==) so PHP is looking for "truthy" statements. So ANY value that is not "falsey" will evaluate your statement (i.e. 0, false, empty strings, NULL). You can find a complete list here.
The best way around this is to use equivalency to ensure it's the exact value you want
if ($this->data[$this->alias]['enabled'] === 1)
That will force PHP to look for an integer of 1. Be aware, though, that your value MUST be the same. In other words
if('1' === 1)
Is always false because string 1 is not the same as integer 1
In PHP, if there is a conditional like this:
if ( is_numeric($my_var) && $my_var == 1 ) {
}
If the first part of the if is false, does the second part ($my_var == 1) get ever executed?
Thanks!
In your example the $my_var == 1 will not be executed (if it's not numeric). PHP will determinate that the first part evaluated to false and so there is no benefit in executing the second part because you are using the && AND operator.
An example:
if(isset($_GET['something']) && $_GET['something'] == '1')
{
}
If the querystring variable something is missing then it doesn't check if it equals 1. If it did then it could produce an Undefined index notice.
You can also verify this behavior with something like:
$test = '2';
if($test == '1' && die('dead'))
{
}
echo 'execution continues....';
Set $test = '2' and the die() will not stop execution. Set it to 1 and the die will execute and stop, thus you won't see Execution continues...
Edit: there is some general information here (not PHP specific).
If the first condition is false second one will not be executed if you use &&. You can try it yourself:
function a(){
echo 'a';
return true;
}
function b(){
echo 'b';
return true;
}
if (a() && b())
{
//do something
}
This will output: ab.
function a(){
echo 'a';
return false;
}
function b(){
echo 'b';
return true;
}
if (a() && b())
{
//do something
}
Outputs a.
I gave you this example because I couldn't find anything in docs but the first comment in this section
This is called a call-by-need or lazy evaluation.
Note: In some cases it's useful or necessary that the second function is executed despite of the state of first condition. In that cases you can use & operator. With bitwise operators you work with numbers, not with booleans. Because php interpretator should know both value before and after & operator it will execute both functions (a() & b()) and true, false are evaluated as 1 and 0, respectively, 1 & 0 => 0 that will be evaluated as false in if statement.
You can use like
if ( is_numeric($my_var)) {
if($my_var == 1)
{
// your code
}
}
So my code in the past needed a variable to run through 2 functions and then return the value as such.
function 1($variable) {
check($variable);
return $variable // either a -1, -2 or true;
}
// pass the return to next function
function 2($variable) {
check($variable);
return $variable // either a -1, -2 or true;
}
On the next check it returns a message to the user as such:
if($variable == -1) // display message
if($variable == -2) // display message
if($variable == true) // display message
Now, per requirement of work the variable must go through a 3rd function check still returning a -1, -2 or true and then go onto the final if statements for display.
Now this is where it gets odd. If I keep it at 2 functions the if statements work, however if I run it through the 3rd check function I need to format my if's like this in order to correctly check the return:
if($variable === -1) // display message
if($variable === -2) // display message
if($variable === true) // display message
Notice I have to add the 3rd '=' symbol. I just can't figure out why this is happening. Is this normal by some PHP law I don't know about or is this a bug?
This is not odd behavior, it's very natural for PHP.
Following expression:
if ($variable == true) {
}
means that PHP will cast left operand to less pretensive type(in this case BOOLEAN) and do comparison after this. Which obviously will result in TRUE if $variable value is not 0 or FALSE or NULL or ''
In second case i.e. === there is strict check value and type of both operands are compared.
The triple equals sign (===) only returns true if the two objects being compared are identical (of the same type and value), not just equal.
For example:
$a = 1;
$b = "1";
echo $a == $b; // True
echo $a === $b; // False
Your code does not show how you call the functions and store returns, there may be a problem. Plus, I suppose you called function 1 and 2 only for illustration because as you know you cant start name of the function with a number.
=== is 'equals exactly' (value and type). Often used for logical tests, because sometimes you need to distinguish 0 from false and 1 from true.