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PHP中如何定义和使用常量_php技巧

May 17, 2016 am 09:06 AM
constant class constant

1.自定义常量

  * 必须用函数define()定义
  * 定义完后其值不能再改变了
  * 使用时直接用常量名,不能像变量一样在前面加$s
 例如:define("PI",3.14);定义一个常量
      $area = PI*R*R; 计算圆的面积
      define("URL","http://www.jb51.net");
      echo "我的网址是:".URL;

2 系统常量:

  FILE :php程序文件名
  LINE :PHP程序文件行数
  PHP_VERSION:当前解析器的版本号
  PHP_OS:执行当前PHP版本的操作系统名称
可以直接拿来使用,例如要查看执行当前PHP版本的操作系统名称,就可以写成 echo PHP_OS

php定义和使用一个类常量

php类常量

我们可以在类中定义常量。常量的值将始终保持不变。在定义和使用常量的时候不需要使用$符号。

常量的值必须是一个定值,不能是变量,类属性或其它操作(如函数调用)的结果。

Its also possible for interfaces to have constants. Look at the interface documentation for examples. 接口(interface)中也可以定义常量。请查看接口的文档获得更多示例。

PHP5.3.0之后,我们可以用一个变量来动态调用类。但该变量的值不能为关键字self, parent 或static。

定义和使用一个类常量

复制代码 代码如下:

class MyClass
{
const constant = ‘constant value';
function showConstant() {
echo self::constant . “ ”;
}
}

echo MyClass::constant . “ ”;

$classname = “MyClass”;
echo $classname::constant . “ ”; // PHP 5.3.0之后

$class = new MyClass();
$class->showConstant();

echo $class::constant.” ”; // PHP 5.3.0之后
?>

Example #2 静态数据示例

复制代码 代码如下:

class foo {
// PHP 5.3.0之后
const bar = bar
EOT;
}
?>
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