Example analysis of PHP var keyword related principles and usage

I see many friends saying that it doesn’t matter whether you use var or not when defining variables in php, but that’s not the case.

Look at the example, if I use var like this:

var $a=123;
echo $a;
//那么程序会提示语法错误，要去掉var这个变量定义才行。直接
$a=123;
echo $a;
//这样才不会报错，php是弱类型语言，所以不声明类型是没问题的。

When can var be used? Please see:

class Test{
var $a=123;//访问控制，这里的var不用就不正常，当然你可以用public protected等关键词代替，来声明成员变量的属性

}
$obj=new Test();
echo $obj->a;
//打印结果：123

If you change var to public, it will work just as well. .

But at this time, if you remove var in the class and there is no access modifier, it will prompt a syntax error.

In fact, after testing, I believe that var is an alias for public and is used to define public properties in a class. However, due to historical issues, var is no longer used now. Later, I checked the php official website and it turned out to be true.

php official explanation:
Class attributes must be defined as one of public, protected, and private. If defined with var, it is considered public.

Note: For compatibility reasons, the method of defining variables using the var keyword in PHP 4 is still valid in PHP 5 (just as an alias for the public keyword). In versions before PHP 5.1.3, this syntax will generate a E_STRICT Warning

Related learning recommendations: PHP Programming from Beginner to Master

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