Key Concepts: Symbol Rules and Common Misuses of PHP Identifiers

Essential knowledge: Symbol rules and common misuse of PHP identifiers, specific code examples are required

Introduction:
PHP is a popular backend Development language, widely used in the field of web development. In PHP, reasonable use of identifiers is very important for code readability and maintainability. This article will introduce the notation rules of PHP identifiers, list some common misuses, and provide specific code examples.

1. Symbol rules for PHP identifiers:
1. Naming rules for identifiers
(1) Identifiers are composed of letters, numbers and underscores. They must start with letters or underscores and cannot start with Start with numbers.
(2) Identifiers are not case-sensitive, but it is recommended to use camel case to improve code readability. For example: $userName.

2. Use of reserved keywords
(1) PHP has some reserved keywords, such as if, for, while, etc., which cannot be used as identifiers.
(2) If you need to use a reserved keyword as an identifier, you can append an underscore after the keyword. For example: $if_, $for_.

3. Naming conflicts between global variables and local variables
(1) Variables defined inside a function are local variables, and their scope is limited to the inside of the function.
(2) Variables defined outside the function are global variables and can be accessed inside the function.
(3) When accessing global variables inside a function, you need to use the global keyword declaration. For example: global $globalVar.

2. Common misuse of PHP identifiers and code examples:
1. Conflict between variable name and function name
Code example:

function getUser(){
   //...
}

$getUser = "Tom";

In the above code, the variable name There is a conflict between $getUser and the function name getUser. To avoid this situation, use a more meaningful variable name, such as $userName.

2. Irregular naming
Code example:

$user_name = "Tom";

In the above code, although the variable name $user_name conforms to the rules of identifiers, it is recommended to use camel case naming and change it to $ userName, improves readability.

3. Confusion between constants and variables
Code example:

const MAX_NUM = 100;

function test(){
   $max_num = 200;
   //...
}

In the above code, there is confusion between the constant MAX_NUM and the variable $max_num. To avoid this, use all uppercase letters for constants.

4. Naming conflict
Code example:

function test(){
   $value = 100;
   //...
}

function anotherTest(){
   $value = 200;
   //...
}

In the above code, the same variable name $value is used in the two functions, which is prone to naming conflicts. To avoid such situations, you should use descriptive variable names and avoid duplication.

3. Summary:
This article introduces the symbol rules of PHP identifiers, lists some common misuses, and provides specific code examples. Proper use of PHP identifiers is very important for code readability and maintainability. I hope that by studying this article, I can increase my understanding of the correct use of PHP identifiers and improve my programming capabilities and code quality.

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