30 lines
874 B
Markdown
30 lines
874 B
Markdown
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---
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title: Constants
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localeTitle: 常量
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---
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## 常量
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常量是PHP中的一种变量。设置常量的`define()`函数有三个参数 - 键名,键的值和布尔值(true或false),它确定键的名称是否不区分大小写(默认为false)。设置后,常量值不能更改。它用于很少更改的值(例如数据库密码或api密钥)。
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### 范围
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重要的是要知道,与变量不同,常量总是具有全局范围,并且可以从脚本中的任何函数访问。
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### 例
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```PHP
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<?php
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define("freeCodeCamp", "Learn to code and help nonprofits", false);
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echo freeCodeCamp;
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```
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**输出:**
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```text
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Learn to code and help nonprofits
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```
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#### 更多信息:
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* [php.net常量手册](https://secure.php.net/manual/en/language.constants.php)
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* [php.net define()手册](https://secure.php.net/manual/en/function.define.php)
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