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PHP变量的定义、可变变量、变量引用、销毁方法

程序员文章站 2022-03-29 17:39:55
复制代码 代码如下:
复制代码 代码如下:

<?php
$long="big_long_variable_name";
$$long="php";     /* 用存放在变量$long里的字符串作为新变量的变量名,等同于$big_long_variable_name="php"; */
$short=& $big_long_variable_name;  /* 取变量$big_long_variable_name的值赋给变量$short,此时$short的值为"php",等同于$short=& $$long; */
print "01 /$short is $short.";   /* "/$"是转义序列,表示输出一个美元符号$,下同。本语句的作用是输出:01 $short is php. */
print "02 long is $big_long_variable_name."; /* 输出:02 long is php. */
?>
<br />
<br />
<?php $big_long_variable_name.=" rocks!"; /* 重新对$big_long_variable_name赋值。重新赋值过程中,由于在$big_long_variable_name的后面添加了.(点号),因而变量$big_long_variable_name此时的值应为原值("php")+新值(" rocks!"),即变量$big_long_variable_name当前完整的值为"php rocks!"。下同。*/
print "03 /$short is $short";   /* 输出:03 $short is php rocks! */
print "04 long is $big_long_variable_name"; /* 输出:04 long is php rocks! */
?>
<br />
<br />
05 $short is php rocks!
06 long is php rocks!
<br />
<br />
<?php $short.="programming $short";   /* 重新对变量$short赋值。由于在$short后面添加了.(点号),因此请参考上例分析$short的值。*/
print "07 /$short is $short";   /* 输出:07 $short is php rocks!programming php rocks! */
print "08 long is $big_long_variable_name"; /* 由于变量$short被重新赋值为programming php rocks!,因而变量$big_long_variable_name的值也与$short一同被改变为"php rocks!programming php rocks!"。本语句输出:08 long is php rocks!programming php rocks!注意,如果是对具有相同值的一个变量进行销毁unset( ),则另一个变量不适用于此种情况,即不会随之被一同销毁。*/
?>
<br />
<br />
09 $short is programming php rocks!
10 long is programming php rocks!
<br />
<br />
<?php $big_long_variable_name.="web programming $short";  /* 变量$big_long_variable_name被重新赋值,此时它完整的值应为php rocks!programming php rocks!web programming php rocks!programming php rocks!。变量$short的值此时与变量$big_long_variable_name一致。请分别参考第5处、第10处注释进行分析。*/
print "11 /$short is $short";     /* 输出:11 php rocks!programming php rocks!web programming php rocks!programming php rocks! */
print "12 long is $big_long_variable_name";
?>
<br />
<br />
<?php
unset($big_long_variable_name);   /* 用unset( )销毁变量$big_long_variable_name,变量$short不会因此受到任何影响。*/
print "13 /$short is $short";   /* 虽然销毁了变量$big_long_variable_name,但$short没有受到影响,它的值仍是最近一次被赋予的php rocks!programming php rocks!web programming php rocks!programming php rocks! */
print "14 long is $big_long_variable_name."; /* 变量$big_long_variable_name已被销毁,故而无值。输出:14 long is. */
snow;                                   
?>
<br />
<br />
<?php $short="no point test1";   /* 重新对变量$short赋值。由于这次没有在$short后面添加.(点号),因此$short当前的值为"no point test1"。*/
print "15 /$short is $short.";   /* 输出:15 $short is no point test1. */
$short="no point test2 $short";   /* 重新对变量$short赋值。没在$short的后面添加.(点号),但引用了它自身最近一次的值"no point test1"。*/
print "16 /$short is $short.";   /* 输出:16 $short is no point test2 no point test1. */