How to determine if a value is in an array in php

In PHP programming, it is often necessary to determine whether a value is in an array. This can usually be achieved using the in_array() function. However, sometimes we need to determine whether a value is not in the array, so how should we do it?

In this article, we will introduce three commonly used methods to determine whether a value is not in an array, as well as their advantages, disadvantages, and applicable scenarios. First, let's take a look at how to use the in_array() function:

in_array($needle, $haystack);

where $needle represents the value to be found, and $haystack represents the array to be searched for. If $needle is in $haystack, the function returns true; otherwise, it returns false.

Then, to determine whether a value is not in the array, you only need to add a negation operation before the result of the in_array() function, as shown below:

!in_array($needle, $haystack);

This way Determine whether $needle is not in $haystack. However, this method has a disadvantage, that is, when $needle is in $haystack, the function will still return false, and the result needs to be inverted again to get the correct answer.

The above method can also be rewritten in the following form:

array_search($needle, $haystack) === false;

The array_search() function is used to find a value in the array. If found, the key of the value in the array is returned; Otherwise, return false. Therefore, if you want to determine that $needle is not in $haystack, you can determine whether the return value of array_search($needle, $haystack) is equal to false.

However, this method also has a disadvantage, that is, if $needle is in $haystack, the function will return the key of the element in the array instead of returning true. Therefore, the results need to be compared again to get the correct answer.

Finally, we introduce a simpler and more effective method, using PHP operators! = and !==, as shown below:

!($value != array_search($needle, $haystack));

The principle of this method is that if $needle is in $haystack, array_search($needle, $haystack) returns the key of the element in the array, $value is equal to the key; otherwise, $value is equal to false. Therefore, you only need to determine whether $value is equal to array_search($needle, $haystack), and then perform the inversion operation to get the correct answer.

In short, in PHP programming, you can use the above three methods to determine whether a value is not in an array. When choosing the appropriate method, you need to consider the specific situation and choose the most suitable method to implement the function.

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