What are the magic constants in php?

Commonly used magic constants are: 1. LINE, the digital representation of the current line number; 2. FILE, the full path and file name of the current file; 3. DIR, the directory where the current file is located; 4. FUNCTION, The name of the current function; 5. CLASS, the name of the current class; 6. TRAIT, the name of the current feature; 7. METHOD, the name of the current method; 8. NAMESPACE, the name of the current namespace, etc.

The operating system for this tutorial: Windows 10 system, PHP8.1.3 version, Dell G3 computer.

In PHP, there are some special predefined constants called "magic constants" whose values ​​will change in different contexts. The following are some commonly used magic constants in PHP:

1. LINE: The numeric representation of the current line number.
2. FILE: The full path and file name of the current file.
3. DIR: The directory where the current file is located.
4. FUNCTION: The name of the current function.
5. CLASS: The name of the current class.
6. TRAIT: The name of the current trait.
7. METHOD: The name of the current method.
8. NAMESPACE: The name of the current namespace.

These magic constants can provide some useful information when writing code, such as for debugging, logging, or dynamically obtaining file paths. Please note that magic constants are not case sensitive.

Example usage:

echo __LINE__; // 输出当前行号
echo __FILE__; // 输出当前文件的路径和文件名
echo __DIR__; // 输出当前文件所在的目录
echo __FUNCTION__; // 输出当前函数的名称
echo __CLASS__; // 输出当前类的名称
echo __TRAIT__; // 输出当前特性（trait）的名称
echo __METHOD__; // 输出当前方法的名称
echo __NAMESPACE__; // 输出当前命名空间的名称

It should be noted that the value of the magic constant may change in different contexts, so you must make a judgment based on the specific context when using it.

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