


The difference and usage examples of define and defined functions in PHP
define
define is used to define a constant, which is also globally scoped. It can be accessed anywhere in the script regardless of scope. Once a constant is defined, it cannot be changed or undefined.
Constants and variables have many similarities, so they are easy to confuse; below, we list the differences between constants and variables:
A constant value cannot be changed after it is specified
When setting a constant, there is no need to add the "$" symbol in front
Constants can Accessed by all ranges of domains
The value of a constant can only be "string [string]" and "number [number]"
The syntax format of define is as follows:
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Parameter | Description |
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name | Required parameter. Specify the name of the constant |
#value | Required parameters. Specify the value of the constant |
case_insensitive | Optional parameter. Specifies whether the name of the constant is case-insensitive. If set to True, letters are not case-sensitive; if set to False, letters are case-sensitive. The default value is: False |
Specify a constant (case-sensitive), the sample code is as follows:
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Output the following results:
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Specify a constant (case-insensitive), the sample code is as follows:
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Output the following results:
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defined
defined is used to detect whether a constant is defined. If the constant exists, it returns true, otherwise it returns false. The syntax format of
defined is as follows:
1 |
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Parameter | Description |
---|---|
name | Required parameters. Specify the name of the constant object |
The sample code is as follows:
1 2 3 4 |
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Output the following results:1
The defined tag of ThinkPHP template engine is used to determine whether a constant has been defined.
The defined tag usage is as follows:
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Use the defined tag in template/Tpl/default/Index/display.html as follows:
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If the judgment is not defined, you can Use:
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