What happens when comparing arrays in PHP

Array is a very important data type in PHP. It is widely used in various scenarios, such as storing data, passing parameters, etc. In many cases, we need to compare two or more arrays to determine whether they are equal. So, what happens when comparing arrays in PHP?

There are two operators for comparing arrays in PHP, namely "==" and "===". The comparison results of these two operators are different. Let's first look at the comparison rules of the "==" operator.

When you use the "==" operator to compare two arrays, it compares each element in the array one by one. Specifically, it first compares whether the number of elements in the two arrays is equal. If the numbers are equal, compare each element one by one, otherwise false is returned directly. During the comparison of elements, if one element in an array is equal to any element in another array, the two elements are considered equal. The equality mentioned here means that the two elements have the same key value and value. They are equal only if the key value and value are the same.

The following is an example that demonstrates the process of using the "==" operator to compare two arrays:

$arr1 = array("apple", "banana", "orange") ;
$arr2 = array("banana", "orange", "apple");

if ($arr1 == $arr2) {

echo "Two arrays are equal.";

} else {

echo "Two arrays are not equal.";

}

The output result is "Two arrays are not equal.". This is because although array $arr1 and array $arr2 contain the same elements, but in different orders, they are not equal according to the comparison rule of the "==" operator.

Next, let’s take a look at the comparison rules of the “===” operator.

When using the "===" operator to compare two arrays, it will first compare whether the references of the two arrays are equal, that is, whether they point to the same array. If they are not the same array, return false directly; otherwise, compare each element for equality according to the rules of the "==" operator.

The following is an example to illustrate the use of the "===" operator.

$arr1 = array("apple", "banana", "orange");
$arr2 = array("apple", "banana", "orange");
$arr3 = &$arr1;

if ($arr1 === $arr2) {

echo "Two arrays are equal.";

} else {

echo "Two arrays are not equal.";

}

if ($arr1 === $arr3) {

echo "Two arrays are the same.";

} else {

echo "Two arrays are not the same.";

}

The output results are "Two arrays are not equal." and "Two arrays are the same." ". This is because although $arr1 and $arr2 contain the same elements, they are not the same array; $arr1 and $arr3 are the same array and point to the same memory space.

In actual programming, we need to choose to use the "==" or "===" operator according to the actual situation. If we need to compare the element values, key names and order in the array, we should use the "==" operator; if we need to compare whether the array is exactly the same, including references, element values, key names and order, we should use the "===" operator symbol.

Finally, it should be noted that when comparing arrays, if the array contains an object, their comparison results are determined by this object. Because object comparison in PHP is based on references, if the object has different references in two arrays, the two arrays will be considered unequal.

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