How to convert string into corresponding operator in php

In PHP development, we often need to dynamically generate some operators based on the string input by the user. For example, when the computer automatically parses the user input into an SQL query statement, the user may use the greater than sign and the less than sign in the query conditions. , equal sign and other operators. At this time, we need to convert these strings into corresponding operators.

So, how to implement this function? In fact, PHP provides us with a simple method: using variable variables and the $_GET array to implement the string conversion operator.

First of all, we need to know that there is a type of variable in PHP called variable variables (Variable variables), which is the variable name of a variable. The syntax is ${$varname}, where $varname is an ordinary variable name. For example, the following example:

$name = 'Tom'; // 定义一个普通的变量$name
$$name = 'Hello'; // 定义一个可变变量$Tom，其变量名为$name的值，即'Tom'
echo $Tom; // 输出'Hello'

Next, we can combine the $_GET array to implement the string conversion operator. The $_GET array is an array used in PHP to receive parameters submitted through GET. For example, when we enter: http://www.example.com/test.php?a=b in the address bar, the value of $_GET['a'] is b.

The following is an example of converting characters into operators:

$operator = $_GET['op']; // 获取用户输入的运算符
$a = 1;
$b = 2;
$result = null;
switch ($operator) {
    case '+':
        $result = $a + $b;
        break;
    case '-':
        $result = $a - $b;
        break;
    case '*':
        $result = $a * $b;
        break;
    case '/':
        $result = $a / $b;
        break;
    default:
        // 不支持的运算符
        break;
}
echo $result; // 输出运算结果

In the above code, we first define the $operator variable to store the operator entered by the user. Next, we define two variables $a and $b. In the switch statement, we use different operators to calculate the results of $a and $b based on the operator entered by the user, and store the results in the $result variable. Finally, we output the result of the operation.

However, when the user enters the strings ' ', '-', '*', '/', the above code will work normally. But if the user enters a completely new operator, the program will error. Therefore, we need a more general way to implement the string conversion operator.

We can use the operator as the variable name of the variable variable, and use $$ followed by the operator name to implement the string conversion operator. In this implementation, $ $op is used as a variable variable, which has four values: '$ $', '$-$', '$*$', '$/$', according to these variable variables For the name, we can implement the string conversion operator.

The following is an example of using variable variables to convert strings into operators:

$op = $_GET['op'];
$a = 1;
$b = 2;
$result = null;

$$op = function($a, $b) {
    return eval("return($a $op $b);"); // 将$op替换为运算符，使用eval执行运算
};

if (isset($$op)) {
    $function = $$op; // 获得对应的函数
    $result = $function($a, $b); // 计算结果
}

echo $result; // 输出运算结果

In the above code, we first define the $op variable to store the operator entered by the user . Next, we define two variables $a and $b. On line 7, we dynamically define an anonymous function based on the operator and store it in the mutable variable $$op. In the if statement, if the variable variable $$op exists, we use the variable variable $function to call the corresponding function to calculate the result, and store the result in the variable $result. Finally, we output the result of the operation.

It should be noted that this implementation method may have some security issues when using the eval function, so it is not recommended to be used in formal projects. In actual development, we can choose to use predefined operators or use custom operators to convert strings into operators.

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