218 lines
4.9 KiB
Markdown
218 lines
4.9 KiB
Markdown
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---
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title: PHP functions
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localeTitle: PHP函数
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---
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PHP函数与其他编程语言类似。函数是一段代码，它以参数的形式接受另一个输入，并进行一些处理并返回一个值。
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您已经看过许多函数，如fopen（）和fread（）等。它们是内置函数，但PHP也为您提供了创建自己的函数的选项。
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有两个部分应该清楚 -
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### 创建PHP函数
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调用PHP函数 实际上你几乎不需要创建自己的PHP函数，因为已经有超过1000个为不同区域创建的内置库函数，你只需要根据你的要求调用它们。
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有关一组完整的有用功能，请参阅PHP函数参考。
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创建PHP函数 它很容易创建自己的PHP函数。假设您要创建一个PHP函数，只需在您调用它时在浏览器上写一条简单的消息。下面的示例创建一个名为writeMessage（）的函数，然后在创建它之后立即调用它。
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请注意，在创建函数时，其名称应以关键字函数开头，并且所有PHP代码都应放在{和}大括号内，如下面的示例所示 -
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```
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<html>
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<head>
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<title>Writing PHP Function</title>
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</head>
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<body>
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<?php
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/* Defining a PHP Function */
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function writeMessage() {
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echo "You are really a nice person, Have a nice time!";
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}
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/* Calling a PHP Function */
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writeMessage();
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?>
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</body>
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</html>
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```
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这将显示以下结果 -
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```
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You are really a nice person, Have a nice time!
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```
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### 带参数的PHP函数
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PHP为您提供了在函数内传递参数的选项。你可以传递尽可能多的参数。这些参数与函数内的变量类似。以下示例采用两个整数参数并将它们一起添加然后打印它们。
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```
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<html>
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<head>
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<title>Writing PHP Function with Parameters</title>
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</head>
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<body>
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<?php
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function addFunction($num1, $num2) {
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$sum = $num1 + $num2;
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echo "Sum of the two numbers is : $sum";
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}
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addFunction(10, 20);
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?>
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</body>
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</html>
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```
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这将显示以下结果 -
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```
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Sum of the two numbers is : 30
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```
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### 通过引用传递参数
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可以通过引用将参数传递给函数。这意味着函数操作对变量的引用而不是变量值的副本。
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在这些情况下对参数所做的任何更改都将更改原始变量的值。您可以通过在函数调用或函数定义中向变量名称添加＆符来通过引用传递参数。
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以下示例描述了两种情况。
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```
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<html>
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<head>
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<title>Passing Argument by Reference</title>
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</head>
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<body>
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<?php
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function addFive($num) {
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$num += 5;
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}
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function addSix(&$num) {
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$num += 6;
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}
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$orignum = 10;
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addFive( $orignum );
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echo "Original Value is $orignum<br />";
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addSix( $orignum );
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echo "Original Value is $orignum<br />";
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?>
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</body>
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</html>
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```
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这将显示以下结果 -
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```
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Original Value is 10
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Original Value is 16
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```
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### PHP函数返回值
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函数可以使用return语句结合值或对象返回值。 return停止执行函数并将值发送回调用代码。
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您可以使用返回数组（1,2,3,4）从函数返回多个值。
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下面的示例采用两个整数参数并将它们一起添加，然后将它们的总和返回给调用程序。请注意，return关键字用于从函数返回值。
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```
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<html>
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<head>
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<title>Writing PHP Function which returns value</title>
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</head>
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<body>
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<?php
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function addFunction($num1, $num2) {
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$sum = $num1 + $num2;
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return $sum;
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}
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$return_value = addFunction(10, 20);
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echo "Returned value from the function : $return_value";
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?>
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</body>
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</html>
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```
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这将显示以下结果 -
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```
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Returned value from the function : 30
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```
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### 设置功能参数的默认值
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如果函数的调用者未传递参数，则可以将参数设置为具有默认值。
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如果use没有将任何值传递给此函数，则以下函数将打印NULL。
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```
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<html>
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<head>
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<title>Writing PHP Function which returns value</title>
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</head>
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<body>
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<?php
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function printMe($param = NULL) {
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print $param;
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}
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printMe("This is test");
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printMe();
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?>
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</body>
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</html>
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```
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这将产生以下结果 -
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```
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This is test
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```
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### 动态函数调用
|
|||
|
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|||
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可以将函数名称作为字符串分配给变量，然后像处理函数名称一样处理这些变量。以下示例描述了此行为。
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|||
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```
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<html>
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<head>
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<title>Dynamic Function Calls</title>
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</head>
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<body>
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<?php
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function sayHello() {
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echo "Hello<br />";
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}
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$function_holder = "sayHello";
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$function_holder();
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?>
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</body>
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</html>
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```
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这将显示以下结果 -
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```
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Hello
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```
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