PHP变量的定义、可变变量、变量引用、销毁方法

$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. */
?>




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! */
?>




05 $short is PHP rocks!
06 Long is PHP rocks!




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。*/
?>




09 $short is Programming PHP rocks!
10 Long is Programming PHP rocks!




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";
?>




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;                                   
?>




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. */