In PHP, how are predefined constants and variables used and output?

Question:

FILE
LINE
TRUE
E_PARSE
Can you give examples of these four constants?

There are other predefined variables, I also want to know how to use them. Hope there are examples.

<?php
echo FILE //这里的FILE是不是[两个_ ]的?
?>

Should the above be output like this? But you can’t see anything after output, only a document name.

Answer 1:

Several PHP "magic constants"

LINE: The current line number in the file.

FILE: The full path and file name of the file. If used in an include file, returns the include file name. As of PHP 4.0.2, FILE always contains an absolute path, while versions before that sometimes contained a relative path.

FUNCTION: Function name (newly added in PHP 4.3.0). Since PHP 5 this constant returns the name of the function as it was defined (case sensitive). In PHP 4 this value is always lowercase.

CLASS: The name of the class (newly added in PHP 4.3.0). Since PHP 5 this constant returns the name of the class when it was defined (case sensitive). In PHP 4 this value is always lowercase.

METHOD: The method name of the class (newly added in PHP 5.0.0). Returns the name of the method as it was defined (case-sensitive).

Answer 2:

LINE: The current line number in the file.

FILE: The full path and file name of the file. If used in an include file, returns the include file name. As of PHP 4.0.2, FILE always contains an absolute path, while versions before that sometimes contained a relative path.

TRUE: TRUE and FALSE are the judgment results in PHP. TRUE means the result is true and FALSE is false.

E_PARSE: First, let’s take a look at the error_reporting function.

error_reporting: Configure Error messageThe level of reporting.

Syntax: int error_reporting(int [level]);

Return value: integer

Function type: PHP system function

Content description: This function Used to configure the level of error message reporting. The parameter level is an integer bitmask (bitmask), see the table below.

Bit mask represents the name
1 E_ERROR
2 E_WARNING
4 E_PARSE
8 E_NOTICE
16 E_CORE_ERROR
32 E_CORE_WARNING

·E_NOTICE represents Normally, it is not logged. It is only used when there is an error in the program, such as trying to access a variable that does not exist, or calling the stat() function to view a file that does not exist.
·E_WARNING is usually displayed, but does not interrupt program execution. This is useful for debugging. For example: calling ereg() with the problematic regular expression.
·E_ERROR is usually displayed and also interrupts program execution. This means that memory configuration or other errors cannot be traced using this mask.
·E_PARSE Parse error from syntax.
·E_CORE_ERROR Similar to E_ERROR, but does not include errors caused by the PHP core.
·E_CORE_WARNING Similar to E_WARNING, but does not include PHP core error warnings.

This should be easy to understand

Finally, I suggest you go to the next PHP manual to master the basic syntax.

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