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php中的常量定义 define() 定义形式：define("常量名"，"常量值"，是否大小不写敏感（默认false）)； 常量名：用大写字母和下划线组成； true：大小写不敏感； false:大小写敏感 事例代码如下： 1 ? php 2 3 define ("DEF_FIRST","first" ); 4 5 define ("DE

php中的常量定义  define()

定义形式：define("常量名"，"常量值"，是否大小不写敏感（默认false）)；

常量名：用大写字母和下划线组成；

true：大小写不敏感；   false:大小写敏感

事例代码如下：

<span> 1</span> <span>php
</span><span> 2</span> 
<span> 3</span>      <span>define</span>("DEF_FIRST","first"<span>);
</span><span> 4</span> 
<span> 5</span>      <span>define</span>("DEF_SECOND","Second",<span>true</span><span>);
</span><span> 6</span> 
<span> 7</span>      <span>echo</span>   DEF_FIRST."<br>"<span>;
</span><span> 8</span> 
<span> 9</span>      <span>echo</span>   DEF_SECONd."<br>";<span>//</span><span>注意小写的d</span>
<span>10</span> 
<span>11</span>      <span>define</span>("DEF_FIRST","false");<span>//</span><span>这句话会报错</span>
<span>12</span> 
<span>13</span>      <span>echo</span>   DEF_FIRST."<br>"<span>; 
</span><span>14</span> 
<span>15</span> ?>

 

输出结果：

<span>1</span> <span>first
</span><span>2</span> <span>Second
</span><span>3</span> 
<span>4</span> Notice: <span>Constant</span> DEF_FIRST already <span>defined</span> in ****<span>on line11
</span><span>5</span> first

 

注：常量不允许重定义！