What are the predefined constants in php

php predefined constants include "__LINE__", "__FILE__", "__DIR__", "__FUNCTION__", "__CLASS__", "__TRAIT__", "__METHOD__" and "__NAMESPACE__", etc. 1. __LINE__: a constant representing the current code line number; 2. __FILE__ a constant representing the full path and file name of the file where the current code is located; 3. __DIR__ representing the directory of the file where the current code is located, etc.

The operating environment of this tutorial: windows10 system, php8.1.3 version, DELL G3 computer.

PHP predefined constants are a set of constants defined in advance in the PHP language. These constants exist by default in the PHP running environment and can be accessed globally. They serve some specific functions and purposes and are very useful and convenient when writing PHP programs. Here are some common PHP predefined constants:

1. __LINE__: A constant representing the current code line number. It returns the line number of the line where the constant is located, which is used for debugging and locating errors.

2. __FILE__: Constants representing the full path and file name of the file where the current code resides. It returns the full path and file name of the file where the constant is located, which is used to locate files and path problems when including other files.

3. __DIR__: A constant indicating the directory of the file where the current code is located. It returns the directory path of the file where the constant is located, which is used to locate the directory where the file is located.

4. __FUNCTION__: A constant representing the current function name. It returns the name of the function in which the constant exists and can be used to get the function name within a function.

5. __CLASS__: A constant representing the current class name. It returns the name of the class in which the constant exists and can be used to get the class name within the class.

6. __TRAIT__: A constant representing the current trait name. It returns the name of the trait in which the constant is contained, which can be used to get the trait name within the trait.

7. __METHOD__: A constant representing the current method name. It returns the name of the method in which the constant is located and can be used to get the method name within the method.

8. __NAMESPACE__: A constant representing the current namespace name. It returns the name of the namespace where the constant is located and is used to obtain the namespace name in the namespace.

In addition to the common predefined constants mentioned above, there are some other predefined constants in PHP, such as:

1. true: A constant representing a true value.

2. false: A constant representing a false value.

3. null: A constant representing a null value.

4. PHP_VERSION: A constant representing the currently running PHP version number.

5. PHP_OS: A constant representing the name of the currently running operating system.

The use of these predefined constants can improve the readability and maintainability of the code, allowing you to quickly locate problems and obtain necessary information. When writing PHP programs, make full use of these predefined constants to better develop and debug PHP code. .

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