常量是php脚本中定义的不会改变的值。函数define()用于定义常量。常量一旦被定义，就不能改变，只能通过常量名访问常量，在常量名前没有符号$
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<?php define("PI",3.1415926);
print PI;
?>Copy after login
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php的恒量
define
php
pi
print
php的常量
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