How to get the name of a variable through php

In PHP, all variables are stored in the HastTable structure of "Symbol Table". The scope of a symbol is associated with the active symbol table. Therefore, there is only one active symbol table at a time.

We want to get the current active symbol table through the get_defined_vars method.

get_defined_vars // 返回所有已定义的变量所组成的数组

Find the variable name based on its value, but be aware that variables with the same value may exist.

Therefore, first save the value of the current variable to a temporary variable, and then assign a unique value to the original variable in order to find the name of the variable. After finding the name, save the value of the temporary variable The value is reassigned to the original variable.

Example 1:

<?php
$a = &#39;100&#39;;
echo &#39;$a name is:&#39;.get_variable_name($a).&#39; value:&#39;.$a; // $a name is: a value: 100
/**
* @param String $var   要查找的变量
* @param Array  $scope 要搜寻的范围
* @param String        变量名称
*/
function get_variable_name(&$var, $scope=null){
	$scope = $scope==null? $GLOBALS : $scope; // 如果没有范围则在globals中找寻
	// 因有可能有相同值的变量,因此先将当前变量的值保存到一个临时变量中,然后再对原变量赋唯一值,以便查找出变量的名称,找到名字后,将临时变量的值重新赋值到原变量
	$tmp = $var;
	
	$var = &#39;tmp_value_&#39;.mt_rand();
	$name = array_search($var, $scope, true); // 根据值查找变量名称
	$var = $tmp;
	return $name;
}
?>

Example 2: Get the variable name defined in the function

<?php
function test(){
$a = &#39;100&#39;;
echo &#39;$a name is:&#39;.get_variable_name($a);
}
test(); // $a name is: undefined
//因为在function中定义的变量globals会找不到
function test2(){
$a = &#39;100&#39;;
echo &#39;$a name is:&#39;.get_variable_name($a, get_defined_vars());
}
test2(); // $a name is: a 
// 将scope设定为 get_defined_vars() 可以找到
?>

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