An in-depth explanation of the equality operator == in PHP

PHP’s equality operator (==) uses loose comparison and does not consider data types when comparing values. Specifically, it: Allows equality of integers and strings. NaN is considered equal only to itself. Inf and -Inf are considered equal to only themselves or each other. Treats null only as equal to itself.

In-depth explanation of the equality operator (==) in PHP

Introduction

In PHP, the equality operator (==) is used to compare two expressions for equality. It is a widely used operator, but its behavior is not always intuitive. This article takes an in-depth look at the == operator, including its syntax, semantics, and practical use cases.

Syntax

== The syntax of the operator is as follows:

$result = $variable1 == $variable2;

where $result is a Boolean variable, indicating the equality of $variable1 and $variable2 .

Semantics

== operator uses loose comparison, which means it does not consider the data type, only the value. The following example illustrates this behavior:

// 整型和字符串的值相等
echo (10 == "10") ? "真" : "假"; // 输出：真

Practical use case

Comparing strings and numbers

if ("Hello" == "Hello") {
  echo "两个字符串相等";
}

Comparing arrays

$array1 = [1, 2, 3];
$array2 = [1, 2, 3];

if ($array1 == $array2) {
  echo "两个数组相等";
}

Attention to exceptions

There are a few cases where the == operator may cause unexpected results. For example:

• NaN: Comparing NaN to any value (including itself) always returns false.
• Inf and -Inf: Comparing Inf or -Inf to any value, including itself, except Inf or -Inf, always returns false.
• null: null is only equal to itself (using ==), regardless of data type.

Conclusion

#== operator is a valuable and powerful tool in PHP, but it is crucial to understand its loose comparison behavior. By carefully considering data types and expected results, you can avoid unexpected results and get the most out of the == operator.

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