PHP variable scope testing

<?php
	$a = 1;
	function test(){
		echo $a;
	}
	test();//$a undefined
?>在外部声明的变量，函数内不会自动调用

<?php
	/*$a = 1;
	function test(){
		$a = 2;
		echo $a;//2
	}
	test();
	echo $a;//1
?>

<?php
	function test(){
		$a = 1;
	}
	test();
	echo $a;//$a undefined
?>

<?php
	/function test(){
		Global $a;
		$a = 1;
	}
	test();
	echo $a;//1
?>在函数中的变量声明为global时在外部可调用

<?php
	Global $a;
	$a = 1;
	function test(){
		echo $a;//undefined
	}
	test();
?>

<?php
	$a = 2;
	function test(){
		Global $a;
		echo $a;//2
		$a++;
	}
	test();
	echo $a;//3
?>

<?php
	define(&#39;A&#39;, 1);
	function test(){
		echo A;//1
	}
	test();
?>使用define后，编译时自动替代

The above has introduced PHP variable scope testing, including aspects of it. I hope it will be helpful to friends who are interested in PHP tutorials.