Table of Contents
前端学PHP之变量、数据类型及作用域,php数据类型
目录
变量
变量定义
变量赋值
数据类型
字符串
整数" >整数
浮点数
布尔型
数组
对象
NULL
资源
作用域
global关键词
static关键词
Home php教程 php手册 前端学PHP之变量、数据类型及作用域,php数据类型

前端学PHP之变量、数据类型及作用域,php数据类型

Jun 13, 2016 am 08:48 AM
php

前端学PHP之变量、数据类型及作用域,php数据类型

目录
[1]变量 变量定义 变量赋值 [2]数据类型 字符串 整数 浮点数 布尔型 数组 对象 NULL 资源 [3]作用域 global static

变量

变量定义

  变量是存储信息的容器,以$符号开头,其后是变量名称。变量名称必须以字母或下划线开头,对大小写敏感

<?<span>php
</span><span>$x</span>=5<span>;
</span><span>//</span><span>5</span>
<span>echo</span> <span>$x</span><span>;
</span><span>//</span><span>什么都不输出</span>
<span>echo</span> <span>$X</span><span>;
</span>?>
Copy after login

变量赋值

  PHP没有创建变量的命令,变量会在首次为其赋值时被创建

<?<span>php
</span><span>$txt</span>="Hello world!"<span>;
</span><span>$x</span>=5<span>;
</span><span>$y</span>=10.5<span>;
</span>?>
Copy after login

数据类型

  PHP是一门类型松散的语言,不必告知PHP变量的数据类型,PHP会根据它的值,自动把变量转换成正确的数据类型。PHP数据类型包括8种:其中包括四种标量类型、两种复合类型和两种特殊类型。具体是:字符串、整数、浮点数、布尔、数组、对象、NULL、资源

  [注意]var_dump() 会返回变量的数据类型和值

字符串

  字符串可以是引号内的任何文本,引号可以是单引号或双引号

<?<span>php 
</span><span>$x</span> = "Hello world!"<span>;
</span><span>//</span><span>Hello world!</span>
<span>echo</span> <span>$x</span><span>;
</span><span>echo</span> "<br>"<span>; 
</span><span>$x</span> = 'Hello world!'<span>;
</span><span>//</span><span>Hello world!</span>
<span>echo</span> <span>$x</span><span>;
</span>?>
Copy after login

<情况1>当字符串中包含引号,有三种解决方案:

  [1]单引号中嵌入双引号

  [2]双引号中嵌入单引号

  [3]使用转义符"\"

<?<span>php 
</span><span>$str_string1</span> = '"test"'<span>;
</span><span>$str_string2</span> = "'test'"<span>;
</span><span>$str_string3</span> = '\'test\''<span>;
</span><span>echo</span> <span>$str_string1</span><span>;
</span><span>echo</span> "<br />"<span>;
</span><span>echo</span> <span>$str_string2</span><span>;
</span><span>echo</span> "<br />"<span>;
</span><span>echo</span> <span>$str_string3</span><span>;
</span>?>
Copy after login

<情况2>当字符串的引号遇到变量,分为两种情况:

  [1]当双引号中包含变量时,变量会与双引号中的内容连接在一起

  [2]当单引号中包含变量时,变量会被当作字符串输出

<?<span>php 
</span><span>$test</span> = 1<span>;
</span><span>$str_string1</span> = ' $test '<span>;
</span><span>$str_string2</span> = " <span>$test</span> "<span>;
</span><span>$str_string3</span> = ' "$test" '<span>;
</span><span>$str_string4</span> = " '<span>$test</span>' "<span>;
</span><span>echo</span> <span>$str_string1</span>;<span>//</span><span>$test</span>
<span>echo</span> "<br />"<span>;
</span><span>echo</span> <span>$str_string2</span>;<span>//</span><span>1</span>
<span>echo</span> "<br />"<span>;
</span><span>echo</span> <span>$str_string3</span>;<span>//</span><span>"$test"</span>
<span>echo</span> "<br />"<span>;
</span><span>echo</span> <span>$str_string4</span>;<span>//</span><span>'1'</span>
?>
Copy after login

<情况3>当字符串很长时,使用Heredoc结构形式的方法,首先定界符表示字符串(<<<),接着在(<<<)之后提供一个标识符(任意名称),换行后是字符串,最后以这个标识符结束字符串。注意标识符左右不要有多余的空格

<?<span>php 
</span><span>$str</span> = <<<<span> G
</span>123<span>
G;
</span><span>echo</span> <span>$str</span>;<span>//</span><span>123</span>
?>
Copy after login

整数

  PHP整数必须至少有一个数字,不能包含逗号或空格,不能有小数点,正负均可,可以用三种格式规定整数:十进制、十六进制(前缀是0x)或八进制(前缀是0)

<?<span>php 
</span><span>$x</span> = 5985<span>;
</span><span>//</span><span>int(5985)</span>
<span>var_dump</span>(<span>$x</span><span>);
</span><span>echo</span> "<br>"<span>; 
</span><span>$x</span> = -345<span>; 
</span><span>//</span><span> int(-345)</span>
<span>var_dump</span>(<span>$x</span><span>);
</span><span>echo</span> "<br>"<span>; 
</span><span>$x</span> = 0x11<span>; 
</span><span>//</span><span> int(17)</span>
<span>var_dump</span>(<span>$x</span><span>);
</span><span>echo</span> "<br>"<span>;
</span><span>$x</span> = 011<span>; 
</span><span>//</span><span> int(9)</span>
<span>var_dump</span>(<span>$x</span><span>);
</span>?>
Copy after login

浮点数

  PHP浮点数是有小数点或指数形式的数字

<?<span>php 
</span><span>$x</span> = 10.365<span>;
</span><span>//</span><span>float(10.365)</span>
<span>var_dump</span>(<span>$x</span><span>);
</span><span>echo</span> "<br>"<span>; 
</span><span>$x</span> = 2.4e3<span>;
</span><span>//</span><span>float(2400)</span>
<span>var_dump</span>(<span>$x</span><span>);
</span><span>echo</span> "<br>"<span>; 
</span><span>$x</span> = 8E-1<span>;
</span><span>//</span><span>float(0.8)</span>
<span>var_dump</span>(<span>$x</span><span>);
</span>?>
Copy after login

布尔型

  PHP布尔型只有两个值:true或false(不区分大小写),常用于条件测试。当用echo指令输出布尔类型时,如果是true,则输出"1",false则什么都不输出

<?<span>php 
    </span><span>$man</span> = "男"<span>;
    </span><span>$flag</span> = <span>$man</span> == "男";<span>//</span><span>输出1</span>
    <span>echo</span> <span>$flag</span><span> ;
    </span><span>echo</span> "<br />"<span> ;
    </span><span>$flag</span> = <span>$man</span> == "女";<span>//</span><span>什么都不输出</span>
    <span>echo</span> <span>$flag</span><span>;
    </span><span>var_dump</span>(<span>$flag</span>);<span>//</span><span>bool(false)</span>
?>
Copy after login

数组

  PHP数组可以在一个变量中存储多个值

<?<span>php 
</span><span>$cars</span>=<span>array</span>("Volvo","BMW","SAAB"<span>);
</span><span>//</span><span>array(3) { [0]=> string(5) "Volvo" [1]=> string(3) "BMW" [2]=> string(4) "SAAB" }</span>
<span>var_dump</span>(<span>$cars</span><span>);
</span>?>
Copy after login

对象

  PHP对象是存储数据和有关如何处理数据的信息的数据类型。在PHP中,必须明确地声明对象,但首先必须声明对象的类。对此,使用class关键词,类是包含属性和方法的结构。然后在对象类中定义数据类型,然后在该类的实例中使用此数据类型

<?<span>php
</span><span>class</span><span> Car
{
    </span><span>var</span> <span>$color</span><span>;
    </span><span>function</span> Car(<span>$color</span>="green"<span>) {
      </span><span>$this</span>->color = <span>$color</span><span>;
    }
    </span><span>function</span><span> what_color() {
      </span><span>return</span> <span>$this</span>-><span>color;
    }
}

</span><span>function</span> print_vars(<span>$obj</span><span>) {
   </span><span>foreach</span> (<span>get_object_vars</span>(<span>$obj</span>) <span>as</span> <span>$prop</span> => <span>$val</span><span>) {
     </span><span>echo</span> "\t<span>$prop</span> = <span>$val</span>\n"<span>;
   }
}

</span><span>$herbie</span> = <span>new</span> Car("white"<span>);
</span><span>echo</span> "\herbie: Properties\n"<span>;
print_vars(</span><span>$herbie</span><span>);
</span>?>
Copy after login

NULL

  PHP中的NULL是空类型,对大小写不敏感,NULL类型只有一个取值,表示一个变量没有值,当被赋值为NULL,或者尚未被赋值,或者被unset(),这三种情况下变量被认为为NULL

<?<span>php 
 </span><span>error_reporting</span>(0); <span>//</span><span>禁止显示PHP警告提示</span>
 <span>$var</span><span>;
 </span><span>var_dump</span>(<span>$var</span>);<span>//</span><span>NULL</span>
 <span>$var1</span> = <span>null</span><span>;
 </span><span>var_dump</span>(<span>$var1</span>);<span>//</span><span>NULL</span>
 <span>$var2</span> = <span>NULL</span><span>;
 </span><span>var_dump</span>( <span>$var2</span>);<span>//</span><span>NULL</span>
 <span>$var3</span> = "节日快乐!"<span>;
 </span><span>unset</span>(<span>$var3</span><span>);
 </span><span>var_dump</span>(<span>$var3</span>);<span>//</span><span>NULL</span>
?>
Copy after login

资源

  PHP资源是由专门的函数来建立和使用的,例如打开文件、数据连接、图形画布。可以对资源进行操作(创建、使用和释放)。任何资源,在不需要的时候应该被及时释放。如果我们忘记了释放资源,系统自动启用垃圾回收机制,在页面执行完毕后回收资源,以避免内存被消耗殆尽

<?<span>php
</span><span>$file</span>=<span>fopen</span>("data/webroot/resource/f.txt","r");   <span>//</span><span>打开文件</span>
<span>$con</span>=<span>mysql_connect</span>("127.0.0.1","root","root");  <span>//</span><span>连接数据库</span>
<span>if</span> (<span>$file_handle</span><span>){
    </span><span>//</span><span>接着采用while循环(后面语言结构语句中的循环结构会详细介绍)一行行地读取文件,然后输出每行的文字</span>
    <span>while</span> (!<span>feof</span>(<span>$file_handle</span>)) { <span>//</span><span>判断是否到最后一行</span>
        <span>$line</span> = <span>fgets</span>(<span>$file_handle</span>); <span>//</span><span>读取一行文本</span>
        <span>echo</span> <span>$line</span>; <span>//</span><span>输出一行文本</span>
        <span>echo</span> "<br />"; <span>//</span><span>换行</span>
<span>    }
}
</span><span>fclose</span>(<span>$file_handle</span>);<span>//</span><span>关闭文件</span>
?>
Copy after login

  [注意]memory_get_usage() 会获取当前PHP消耗的内存,单位为byte

<?<span>php 
</span><span>echo</span> <span>$m1</span> =<span> memory_get_usage(); 
</span><span>echo</span> "<br />"<span>;
</span><span>$var_string</span> = '123';<span>//</span><span>320</span>
<span>echo</span> <span>$m2</span> = memory_get_usage()-<span>$m1</span><span>; 
</span><span>echo</span> "<br />"<span>;
</span><span>$n</span> = 123;<span>//</span><span>272</span>
<span>echo</span> <span>$m3</span> = memory_get_usage()-<span>$m1</span>-<span>$m2</span><span>; 
</span><span>echo</span> "<br />"<span>;
</span><span>$f</span> = 123.00;<span>//</span><span>272</span>
<span>echo</span> <span>$m4</span> = memory_get_usage()-<span>$m1</span>-<span>$m2</span>-<span>$m3</span><span>; 
</span><span>echo</span> "<br />"<span>;
</span><span>$var_array</span> = <span>array</span>('123');<span>//</span><span>576</span>
<span>echo</span> <span>$m5</span> = memory_get_usage()-<span>$m1</span>-<span>$m2</span>-<span>$m3</span>-<span>$m4</span><span>; 
</span>?>
Copy after login
<?<span>php 
  </span><span>$string</span> = "就是就是"<span>;
 </span><span>var_dump</span>(<span>$string</span>);<span>//</span><span>string(12) "就是就是"</span>
 <span>echo</span> "<br />"<span>;
 </span><span>$string</span> = 9494<span>;
 </span><span>var_dump</span>(<span>$string</span>);<span>//</span><span>int(9494)</span>
  <span>echo</span> "<br />"<span>;
</span>?>
Copy after login

作用域

  PHP有三种不同的变量作用域:local(局部)、global(全局)、static(静态)

  函数之外声明的变量有global作用域,只能在函数以外进行访问;函数内部声明的变量有local作用域,只能在函数内部进行访问

<?<span>php
</span><span>error_reporting</span>(0); <span>//</span><span>禁止显示PHP警告提示</span>
<span>$x</span>=5; <span>//</span><span> 全局作用域</span>

<span>function</span><span> myTest() {
  </span><span>$y</span>=10; <span>//</span><span> 局部作用域</span>
  <span>echo</span> "<p>测试函数内部的变量:</p>"<span>;
  </span><span>echo</span> "变量 x 是:<span>$x</span><br>"<span>;
  </span><span>echo</span> "变量 y 是:<span>$y</span>"<span>;
} 
</span><span>//</span><span>无输出
//10</span>
<span>myTest();
</span><span>echo</span> "<p>测试函数之外的变量:</p>"<span>;
</span><span>echo</span> "变量 x 是:<span>$x</span><br>";<span>//</span><span>5</span>
<span>echo</span> "变量 y 是:<span>$y</span>";<span>//</span><span>无输出</span>
?>
Copy after login

global关键词

  用于访问函数内的全局变量

<?<span>php
</span><span>$x</span>=5<span>;
</span><span>$y</span>=10<span>;

</span><span>function</span><span> myTest() {
  </span><span>global</span> <span>$x</span>,<span>$y</span><span>;
  </span><span>$y</span>=<span>$x</span>+<span>$y</span><span>;
}

myTest();
</span><span>echo</span> <span>$y</span>; <span>//</span><span> 输出 15</span>
?>
Copy after login

  PHP同时在名为GLOBALS[index]的数组中存储了所有的全局变量,下标存有变量名。这个数组在函数内也可以访问,并能够用于直接更新全局变量

<?<span>php
</span><span>$x</span>=5<span>;
</span><span>$y</span>=10<span>;

</span><span>function</span><span> myTest() {
  </span><span>$GLOBALS</span>['y']=<span>$GLOBALS</span>['x']+<span>$GLOBALS</span>['y'<span>];
} 

myTest();
</span><span>echo</span> <span>$y</span>; <span>//</span><span> 输出 15</span>
?>
Copy after login

static关键词

  通常,当函数完成或执行后,会删除所有变量,不过,有时需要不删除某个局部变量。要完成这一点,需要在首次声明变量时使用static关键词。每当函数被调用时,这个变量所存储的信息都是函数最后一次被调用时所包含的信息,但要注意的是,这个变量仍然是函数的局部变量

<?<span>php
</span><span>function</span><span> myTest() {
   </span><span>static</span> <span>$x</span>=0<span>;
   </span><span>echo</span> <span>$x</span><span>;
   </span><span>$x</span>++<span>;
}

myTest();</span><span>//</span><span>0</span>
<span>echo</span> "<br>"<span>;
myTest();</span><span>//</span><span>1</span>
<span>echo</span> "<br>"<span>;
myTest();</span><span>//</span><span>2</span>
<span>echo</span> "<br>"<span>;
myTest();</span><span>//</span><span>3</span>
<span>echo</span> "<br>"<span>;
myTest();</span><span>//</span><span>4</span>
?>  
Copy after login

 

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Best Graphic Settings
2 weeks ago By 尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

CakePHP Project Configuration CakePHP Project Configuration Sep 10, 2024 pm 05:25 PM

In this chapter, we will understand the Environment Variables, General Configuration, Database Configuration and Email Configuration in CakePHP.

PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian Dec 24, 2024 pm 04:42 PM

PHP 8.4 brings several new features, security improvements, and performance improvements with healthy amounts of feature deprecations and removals. This guide explains how to install PHP 8.4 or upgrade to PHP 8.4 on Ubuntu, Debian, or their derivati

CakePHP Date and Time CakePHP Date and Time Sep 10, 2024 pm 05:27 PM

To work with date and time in cakephp4, we are going to make use of the available FrozenTime class.

CakePHP File upload CakePHP File upload Sep 10, 2024 pm 05:27 PM

To work on file upload we are going to use the form helper. Here, is an example for file upload.

CakePHP Routing CakePHP Routing Sep 10, 2024 pm 05:25 PM

In this chapter, we are going to learn the following topics related to routing ?

Discuss CakePHP Discuss CakePHP Sep 10, 2024 pm 05:28 PM

CakePHP is an open-source framework for PHP. It is intended to make developing, deploying and maintaining applications much easier. CakePHP is based on a MVC-like architecture that is both powerful and easy to grasp. Models, Views, and Controllers gu

CakePHP Working with Database CakePHP Working with Database Sep 10, 2024 pm 05:25 PM

Working with database in CakePHP is very easy. We will understand the CRUD (Create, Read, Update, Delete) operations in this chapter.

CakePHP Creating Validators CakePHP Creating Validators Sep 10, 2024 pm 05:26 PM

Validator can be created by adding the following two lines in the controller.

See all articles