php的数据类型和变量的作用域
1)php支持如下所示的基本数据类型:
Integer(整数)、Float(浮点数)、String(字符串)、Boolean(布尔值)、Array(数组)、Object(对象),此外还有两个特殊的类型:NULL(空)、resource(资源)。
注:没有被赋值、已经被重置或者被赋值为特殊值NULL的变量就是NULL类型的变量。
特定的内置函数(例如数据库函数)将返回resource类型的变量。
2)作用域是指在一个脚本中某个变量可以使用或可见的范围。PHP具有6项基本的作用域规则:
2.1)内置超级全局变量可以在脚本的任何地方使用和可见;
2.2)常量,一旦被声明,将可以在全局可见;
2.3)在一个脚本中声明的全局变量在整个脚本中是可见的;
2.4)函数内部使用的变量声明为全局变量时,其名称要与全局变量名称一致;
2.5)在函数内部创建并声明为静态的变量无法在函数外部可见,但是可以在函数的多次执行过程中保持该值;
2.6)在函数内部创建的变量对函数来说是本地的,当函数终止时,该变量也就不存在了。
注:超级全局变量的完整列表如下所示:
$GLOBALS——所有全局变量数组;
$_SERVER——服务器环境变量数组;
$_GET——通过GET方法传递给该脚本的变量数组;
$_POST——通过POST方法传递给该脚本的变量数组;
$_COOKIE——cookie变量数组;
$_FILES——与文件上传相关的变量数组;
$_ENV——环境变量数组;
$_REQUEST——所有用户输入的变量数组,包括$_GET、$_POST和$_COOKIE所包含的输入内容;
$_SESSION——会话变量数组。
版权声明:本文为博主原创文章,未经博主允许不得转载。

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