The difference between == and == in PHP is that: == is a loose comparison, only the values ??are compared and type conversion is performed, for example, 0=="0" is true; while === is a strict comparison, which compares both values ??and types, such as 0==="0" is false. Common type conversion rules include converting a string to a number when compared to a number, converting a Boolean value to 0 or 1, etc. It is recommended to use === first to avoid unexpected errors. For example, when checking the return value of strpos(), you must use === to determine whether it is false.

In PHP, == and === are operators used for comparison, but their behavior is obviously different. Simply put:

• == is "equal", only values ??are compared, not types.
• === is "all equal to", which compares both values ??and types.

This means that in some cases, using == may return unexpected results due to type conversion.

What is a loose comparison ( == )?

When the == operator compares two variables, it will perform type conversion first and then compare their values. This behavior is called "loose comparison".

for example:

 0 == "0" // true
0 == false // true
"5" == 5 // true
null == "" // true

These results may seem a bit strange, but in fact they are because PHP automatically performs type conversion behind the scenes. For example, "5" == 5 holds true because the string "5" is converted to the integer 5 .

Common type conversion rules include:

• When strings and numbers are compared, PHP tries to convert strings to numbers.
• When a Boolean value participates in the comparison, true will be treated as 1 and false will be treated as 0 .
• null may be considered "equal" when comparing with empty strings, empty arrays, etc.

What is a strict comparison ( === )?

=== Not only compare values, but also requires that the two variables have exactly the same type before returning true . It does not do any type conversion.

for example:

 0 === "0" // false
0 === false // false
"5" === 5 // false
null === "" // false

In this case, the result is false even if the values ??are the same but the types are different. This method is safer and can avoid unexpected behaviors caused by type conversion.

When should I use which one?

Generally speaking, unless you explicitly need to take advantage of the type conversion feature, it is recommended to use === first. It can make your code more logical and reduce potential bugs.

Examples of applicable scenarios:

• The case of using == : You need to relax and determine whether the user input is empty (such as "" == 0 or null == 0 ), but in this case it is better to handle the type manually.
• When using === : you are checking whether the return value of the function is false . For example, if strpos() returns false , it means that it is not found. If you use == an error will occur.

An example that is easy to ignore

For example, the following code:

 if ("abc" == 0) {
    echo "This is true!";
}

This conditional judgment will output "This is true!". Because PHP converts the string "abc" to a number and gets 0 , so == thinks they are equal. If you use === , this problem will not be triggered.

Basically that's it. Understanding the difference between these two operators can help you write more stable and reliable PHP code.

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