What is the relationship between loading order and execution order of PHP functions?

PHP function loading order is determined by the declaration order, including functions defined in the script, included files, and functions imported into the namespace; the execution order is determined by the order of function calls, and the function calls in the script are executed in sequence.

Loading order and execution order of PHP functions: Detailed explanation

Theoretical basis

Loading order of functions refers to the order in which the PHP engine looks for function definitions when parsing the script. The execution order of functions refers to the order in which these functions are called during script execution.

In PHP, the order of function loading is determined by the order of their declarations :

• Functions defined in the script are loaded first
• and then those containing Functions in files in include or require statements
• Functions in namespaces that were last loaded in scripts with use statements

The execution order is determined by the order of function calls. Function calls in the script are executed sequentially. This means that the code within the function will be executed from where it is called, regardless of where it is declared.

Practical case

In order to understand the relationship between loading order and execution order, the following is a sample script:

<?php
// 函数 1：在脚本中声明
function myFunction1() {
    echo "函数 1 已被调用。<br>";
}

// 包含另一个文件
include "another.php";

// 函数 2：在另一个文件中定义
function myFunction2() {
    echo "函数 2 已被调用。<br>";
}

// 函数 3：导入命名空间
use MyNamespace\MyFunction3;

// 函数调用
myFunction1();
myFunction2();
MyFunction3();

Execution process :

1. The PHP engine parses the script and loads the functions in the following order:

   • myFunction1 (declared in the script)
   • myFunction2 (declared in another file)
   • MyNamespace\MyFunction3 (imported from namespace)

2. During script execution, functions are called in the following order:

   • myFunction1
   • myFunction2
   • MyNamespace\MyFunction3

#This example demonstrates that the loading order of functions is determined by the order in which they are declared, and the execution order is determined by the order in which the functions are called. Therefore, regardless of the order in which functions are loaded, they will be executed as soon as they are called.

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