java程序员学php – 8. 神奇的extract()
声明这样一个关联数组: $map[‘BJ’] = ‘Beijing’; $map[‘SH’] = ‘Shanghai’; 然后做一下extract($map), 你就可以自动获得 $BJ 和 $SH这两个变量,它们的值分别为Beijing和Shanghi。 也就是说,extract替你编程了。这在Java语言里还是很难想象的。
声明这样一个关联数组: $map[‘BJ’] = ‘Beijing’; $map[‘SH’] = ‘Shanghai’; 然后做一下extract($map), 你就可以自动获得 $BJ 和 $SH这两个变量,它们的值分别为Beijing和Shanghi。 也就是说,extract替你编程了。这在Java语言里还是很难想象的。
如: $map[‘BJ’] = ‘Beijing’; $map[‘SH’] = ‘Shanghai’; 遍历这个关联数组: foreach($map as $abbr=>$full_name){ echo "$abbr is short for $full_name"; }
foreach($some_array as $element){ echo $element; }
isset($a): 判断一下这个变量是否已经定义 unset($a): destroy a variable
1.gettype()拿到数据类型 比如 gettype(345); //返回"integer" gettype(some_object);// 返回"object" 另有一些快捷的类型查询函数,如 is_double(), is_array(), is_string()等 2.settype()则强行改变数据的类型 settype($a, ‘double’);
3 == ‘3’ ? true 3 === ‘3’ ? False. 两边的值相等且类型相等,才叫恒等,比如3===3
只要数据不是0,那它就可以当作true来用; 否则,就当作false来用。 if("abc") { echo "abc"; //will print "abc" } if(!"0"){ echo "zero"; //will print "zero" }
1. php里的数据类型是动态的,不要求在使用变量之前声明变量,如 $var = 0; 2. php里变量的数据类型可在运行时变换,比如,你可以先后如下赋值: $var = 5; $var = ‘abc’; 不会报错
摘自"Dive into Python" statically typed language A language in which types are fixed at compile time. Most statically typed languages enforce this by requiring you to declare all variables with their datatypes before using them. Java and C are statically typed languages. dynamically typed language A language in which types are discovered at …
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