What are the basic knowledge for getting started with PHP functions?

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What are the basic knowledge for getting started with PHP functions?

The basic knowledge of getting started with PHP functions are:

1. Function declaration

function 函数名([参数1,参数2...])
{
函数体;
return 返回值;
}

2 , Use a double-layer for loop to output the table

function table(){
echo "<table align=&#39;center&#39; border=&#39;1px&#39; width=&#39;600px&#39;>";
echo "<caption><h1 id="通过函数输出表格">通过函数输出表格</h1></caption>";
for($out=0;$out<10;$out++){
$bgcolor = $out%2 == 0 ? "#FFFFFF" : "#DDDDDD";
echo "<tr bgcolor=".$bgcolor.">";
for($in=0;$in<10;$in++){
echo "<td>".$out*10+$in."</td>";
}
echo "</tr>";
}
echo "</table>";
}

3. Rewrite the function tabel()

function table($tableName,$rows,$cols){
echo "<table align=&#39;center&#39; border=&#39;1px&#39; width=&#39;600px&#39;>";
echo "<caption><h1 id="tableName">$tableName</h1></caption>";
for($out=0;$out<$rows;$out++){
$bgcolor = $out%2 == 0 ? "#FFFFFF" : "#DDDDDD";
echo "<tr bgcolor=".$bgcolor.">";
for($in=0;$in<$cols;$in++){
echo "<td>".($out*$cols+$in)."</td>";
}
echo "</tr>";
}
echo "</table>";
}
table("此时你是我的唯一",5,3);

4. The range of PHP variables (divided into Local variables and global variables)

Local variables are also called internal variables. They are variables declared inside a function, and their scope is limited to the inside of the function.

      Local variables can be divided into dynamic storage types and static storage types in terms of storage methods. Local variables in a function, if specifically declared as a static storage category, will allocate storage space dynamically by default.

The internal dynamic variables are automatically released after the function call. If you want the internal variables to remain in memory after the function is executed, you should use static variables. After the function is executed, the static variables will not disappear, but are shared among all calls to the function. That is, when the function is executed again, the static variables will continue to operate from the previous results, and will only be used during the execution of the script. The period function is initialized the first time it is called. To declare a function variable as static, the keyword static is required. Understand it yourself!

function demo($one){
$two = $one;
echo "在函数内部执行:$two+$one=".($two+$one)."<br/>";
}
demo(200);
echo "在函数外部执行:$two+$one=".($two+$one);   //非法访问

Global variables are also called external variables, which are defined outside the function. They start from the definition of their scope variables and end at the end of this program text.

If you want to use a global variable in a function, you must use the global keyword to define the target variable to tell the function body that this variable is a global variable.

$one = 200;
$two = 100;
function demo(){
//在函数内部使用global关键字加载全局变量$one和$two
global $one,$two;
echo "运算结果:$two+$one=".($two+$one)."<br/>"; //300
echo "运算结果:".($GLOBAL[&#39;two&#39;]+$GLOBAL[&#39;one&#39;])."<br/>"; 
 
}

5. Types of PHP function parameters

(1) Functions with regular parameters

string example(string name,int age,double height)

(2) Functions with pseudo-type parameters:

PHP pseudo-types: mixed number callback Three types

mixed funName(mixed $args)

number funName(number $args)

(3) Function that refers to parameters:

If there are parameters modified with "&" in the formal parameters of the function, the function is called A variable must be passed to this parameter instead of a value.

void funName(array $&arg)

(4) Functions with default parameters:

The default value must be a constant expression, not a variable , class members or function calls. PHP allows using arrays and the special type NULL as default parameters.

mixed funName(string name[,string value[,int age]]) // 在参数列表中出现使用[]描述的参数
function person($name="张三",$age=20,$sex="男"){
echo "我的名字是:{$name},我的年龄是{$age},我的性别是{$sex}<br/>";
}

(5) Function with variable number of parameters:

func_get_args();//Return all parameters of the function passed to the script as an array

func_num_args();//Return the total number of parameters

mixed func_get_arg(int $arg_num);//Return a certain number in the parameter list Item (0...)

(6)mixed funName(string arg[,string ...])Callback function: The function parameter is a function

mixed funName(callback arg) //Use pseudo-type callback in the parameter list to describe the variable function, use the variable function declaration and apply the callback function, with the help of call_user_func_array() function customization Callback functions, class static functions and object method callbacks;

//变量函数不能用于语言结构，例如echo()
//print()、unset()、isset()、empty()
//include()、require()及类似的语句       
        function one($a,$b){
return $a+$b;
}
function two($a,$b){
return $a+$b+$b*$b;
}
function three($a,$b){
rerurn $a*$a*$a+$b*$b*$b;
}
$result = "one";
//$result = "two";
//$result = "three";
echo $result(1,2);

function filter($fun){
$fun();
}
function test(){
echo "haha!";
}
function test2(){
echo "houhou!";
}
filter("test");
filter("test2");//haha!houhou!

function fun($msg1,$msg2){
echo '$msg1='.$msg1;
echo &#39;<br/>&#39;;
echo &#39;$msg2=&#39;.$msg2;
}
call_user_func_array(&#39;fun&#39;,array(&#39;Lamp&#39;,&#39;兄弟连&#39;));

//类静态调用和对象的方法调用
class Demo{
static function fun($msg1,$msg2){
echo '$msg1='.$msg1;
echo &#39;<br/>&#39;;
echo &#39;$msg2=&#39;.$msg2;
}
}
class Test{
function fun($msg1,$msg2){
echo &#39;$msg1=&#39;.$msg1;
echo &#39;<br/>&#39;;
echo &#39;$msg2=&#39;.$msg2;
}
}
//类静态调用
call_user_func_array(array(&#39;Demo&#39;,&#39;fun&#39;),array(&#39;Lamp&#39;,&#39;兄弟连&#39;));
//对象的方法调用
call_user_func_array(array(new Test(),&#39;fun&#39;),array(&#39;Lamp&#39;,&#39;兄弟连&#39;));

callback("function name string"); //Callback global function

callback(array("Class name string", "Static method name string in class"));//Call back the static member method in the class

callback(array(Object reference, "Method name string in object");//Static member method in callback object

Recursive function: function calls itself

6. Use self Defining a function library

Function library is not a PHP syntax for defining functions, but a design pattern during programming. Functions are modules of structured programming and are the most important core to achieve code reuse .In order to better organize the code so that customized functions can be used in multiple files in the same project, multiple customized functions are usually organized into the same file or multiple files. These files collect function definitions It is the created PHP function library. If you want to use the functions defined in these files in a PHP script, you need to use a function among include, require, include_once, and require_once to load the function library file into the script program.

The include and require statements both include and run the specified file. The difference is that for the include statement, the file must be read and evaluated every time when executing it; while for require, the file only

is processed once (in fact, the file content replaces the require statement), which means that if the code may be executed multiple times, it is more efficient to use require. In addition, if you read a different file each time the code is executed, or have a loop that iterates through a set of

files, use the include statement.

require is used like require("MyRequireFile.php");. This function is usually placed at the front of the PHP program. Before the PHP program is executed, it will first read in the file specified by require and make it a part of the PHP program web page. Commonly used functions can also be introduced into web pages in this way.

include Use methods such as include("MyIncludeFile.php");. This function is generally placed in the processing part of flow control. The PHP program webpage only reads the include file when it reads it. In this way, the process of program execution can be simplified.

The two of them have exactly the same purpose, and it does not necessarily have to be which one is placed at the front and which one is placed in the middle. The most fundamental difference between them is the way they handle errors.

require If there is an error in a file, the program will interrupt execution and display a fatal error

include If there is an error in a file, the program will not end but will continue to execute. and displays a warning error.

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