#Php foreach empty array how to#
#Php foreach empty array code#

So I have a list of numbers (in PHP, we use the array language construct to contain and identify a list), and each iteration through it we’re seeing a number, which we’re showing to ourselves via an echo command. Here’s our for loop, made into a simple foreach. Rather than going through an abstract sequence you iterate over a pre-set thing.

I’ve always found PHP foreach loops much simpler to understand. If you’ve never seen this syntax before though, it’s a lot to wrap your head around.

#Php foreach empty array code#

What’s great about this code is that if you’ve seen a for loop before (with its weird three-clause syntax of “start condition”, “continue condition”, “per loop operation”), this reads quite simply. You’ll probably use a for loop, like this: for ($x = 1 $x ' Let’s say you want a segment of code to run 20 times. In PHP, you’ll use a for loop mostly when you want to iterate through a set of numbers. But before we get too deep on the foreach loop I do think there’s value in covering how these two popular things differ. PHP improves on the for loop with the foreach loop.

So the above logic is flawed.Anyone who’s programmed much in any language has heard of a for loop. But, as discussed, isset($data) will also return false if $data was set, but was set to null. The author of this code presumably wanted to check if keyShouldBeSet was set in $data. do something here if 'keyShouldBeSet' is not set This behavior is more problematic than it might appear at first and is a common source of problems.Ĭonsider the following: $data = fetchRecordFromStorage($storage, $identifier) Unset($value) // $value no longer references $arrĬommon Mistake #2: Misunderstanding isset() behaviorĭespite its name, isset() not only returns false if an item does not exist, but also returns false for null values. To still get the benefit of using references in foreach loops without running the risk of these kinds of problems, call unset() on the variable, immediately after the foreach loop, to remove the reference e.g.: $arr = array(1, 2, 3, 4) Pass 3: Copies $array (which now equals “2”) into $value (which is a reference to $array), so $array still equals 2.Pass 2: Copies $array (i.e., “2”) into $value (which is a reference to $array), so $array now equals 2.Pass 1: Copies $array (i.e., “1”) into $value (which is a reference to $array), so $array now equals 1.As a result, here’s what happens during each step of the second foreach loop: Specifically, since $value is now being accessed by value (i.e., by copy), foreach copies each sequential $array element into $value in each step of the loop. The last value on the last line is indeed a 2, not a 3.Īfter going through the first foreach loop, $array remains unchanged but, as explained above, $value is left as a dangling reference to the last element in $array (since that foreach loop accessed $value by reference).Īs a result, when we go through the second foreach loop, “weird stuff” appears to happen. The above code will output the following: 1,2,3 Here’s an example of the kind of evasive and confusing bugs that this can lead to: $array = įoreach ($array as &$value) // by value (i.e., copy)

After the loop completes, therefore, $value still points to the last element of $array and remains in scope. On each iteration foreach sets the reference to point to the next element of $array. Thus, $value in the above example is a reference within the top scope of the script. The main thing to remember is that foreach does not create a scope. Subsequent operations involving $value could therefore unintentionally end up modifying the last element in the array. Specifically, in the above example, after the code is executed, $value will remain in scope and will hold a reference to the last element in the array. The problem is that, if you’re not careful, this can also have some undesirable side effects and consequences.

#Php foreach empty array how to#

Not sure how to use foreach loops in PHP? Using references in foreach loops can be useful if you want to operate on each element in the array that you are iterating over. Common Mistake #1: Leaving dangling array references after foreach loops This article highlights ten of the more common mistakes that PHP developers need to beware of. But its ease of use notwithstanding, PHP has evolved into quite a sophisticated language with many frameworks, nuances, and subtleties that can bite developers, leading to hours of hair-pulling debugging. Each element value of the array will be stored in a variable in each iteration. PHP makes it relatively easy to build a web-based system, which is much of the reason for its popularity. It can be used to read both numeric and associative arrays.