What are magic constants in PHP?

With the continuous development of Internet technology, the demand for websites and applications is increasing. Among them, PHP, as an important tool for web development, is gradually becoming well-known. In PHP, we often hear something about "magic constants", so what are magic constants in PHP?

Magic constants are predefined constants whose values ​​are determined when the PHP script is compiled. Magic constants start and end with two underscores, such as LINE__, __FILE, CLASS, etc. These constants represent different meanings. The following are some commonly used magic constants:

LINE: the current line number
FILE: the full path of the current file and File name
DIR: The full path of the directory where the current file is located
FUNCTION: The name of the current function
CLASS: The name of the current class
METHOD: The name of the current method
NAMESPACE: The name of the current namespace

These constants can help us obtain all the information more quickly and accurately. Information is required. For example, we can use the LINE constant to get the line number of the current code. When debugging code, we can use this information to find out where the error is, so we can fix the problem more efficiently.

In addition to the commonly used magic constants listed above, there are many other magic constants in PHP, and their functions are different. For example, the __DIR__ constant can help us quickly get the directory where the current file is located, and the NAMESPACE constant can be used to get the name of the current namespace.

It should be noted that since the values ​​of magic constants are determined at compile time, their values ​​will not change while the code is running. This means that if we change the value of these constants during the execution of the script, the program will not react in any way to this change.

In addition to magic constants, PHP also has some other constants whose values ​​can be changed during script execution. For example, the define() function can be used to define a constant whose value we can change at any time. Unlike magic constants, the names of such constants generally do not begin and end with double underscores.

In general, magic constants in PHP are a convenient and efficient way to help developers obtain the required information more quickly. As long as we are proficient in the use of these constants, we will be more comfortable in the development process.

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