How are PHP functions executed on the server side?

PHP function execution process on the server side: parse the request and determine that the page contains PHP code; start the PHP interpreter, load and parse the script; compile the instructions into opcode; execute the opcode, generate a response; send the response back to the browser.

Server-side execution process of PHP function

PHP is a scripting language that is executed on the server side. When a web page containing PHP code is requested, the code is interpreted and executed by the PHP interpreter on the web server. The execution process is as follows:

1. Parse the request: The Web server receives the HTTP request from the browser and determines that the requested page contains PHP code.
2. Start the PHP interpreter: The web server starts the PHP interpreter, which is a program responsible for executing PHP code.
3. Loading and parsing scripts: The PHP interpreter loads a script file containing PHP code and parses it into a set of source code instructions.
4. Compilation instructions: Source code instructions are compiled into an intermediate code called an opcode. Opcodes are machine instructions that are optimized to execute faster.
5. Execute opcode: The virtual machine of the Web server executes the opcode and performs corresponding operations according to the instructions.
6. Generate response: The PHP interpreter generates a response that contains HTML code or other data to be sent to the browser after executing the PHP code.
7. Send response: The web server sends the response from the PHP interpreter back to the browser.

Practical case:

Let us create a simple PHP script (index.php) that calculates two The sum of numbers and outputs the result:

<?php
// 接收来自表单提交的数字
$num1 = $_POST['num1'];
$num2 = $_POST['num2'];

// 计算总和
$sum = $num1 + $num2;

// 输出结果
echo "总和为：$sum";
?>

When the user submits the form containing this script, the following steps will occur:

1. The Web server starts the PHP interpreter.
2. The PHP interpreter loads and parses the index.php script.
3. The PHP interpreter reads the num1 and num2 values ​​from the form submission.
4. The PHP interpreter calculates the sum and stores it in $sum.
5. The PHP interpreter generates an HTML response containing text representing the sum.
6. The web server sends the response back to the browser.

So executing a PHP function on the server side is about parsing the PHP code into a series of instructions, executing those instructions to perform the code's logic, and generating a response to send back to the browser.

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