163 lines
3.2 KiB
Markdown
163 lines
3.2 KiB
Markdown
---
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title: Learn About Php Variables
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localeTitle: 了解Php变量
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---
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变量是用于存储数据的容器，例如`strings` ， `integers` ， `boolean`值， `array`和对象。
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PHP遵循某些变量声明规则，例如：
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* 变量必须以美元符号（$）开头
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例：
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`php <?php $var = 5; ?>`
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* 变量名称可以包含字符，如AZ，az，0-9，\_和[ASCII](http://www.asciitable.com/ "ASCII Table")字符127-255。
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例：
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`php <?php $var = 5; //Valid $var_1 = "Foo"; //Valid $_var2 = 'Bar'; //Valid $var.3 = 'Baz'; //Invalid ?>`
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* 变量名称可以以下划线（\_）开头。
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例：
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`php <?php $_var2 = 'Bar'; //Valid ?>`
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* 变量名称不能以数字0-9开头。
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例：
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`php <?php $9var3 = 'Baz'; //Invalid ?>`
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* 变量名称区分大小写。
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例：
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```
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<?php
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$var = 5; //Valid
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$VAR = "Foo"; //Valid
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echo $var; //Output 5
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echo "<br>";
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echo $VAR; //Output Foo
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?>
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```
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PHP是一种松散类型的语言，因此在声明变量时我们不需要声明变量的数据类型。与Java或C.不同
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```
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<?php
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$var = 5;
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$var2 = 4;
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$sum = $var+$var2;
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echo $sum; //Output 9
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echo "<br>";
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echo $var+$var2; //Output 9
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?>
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```
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也可以通过引用来分配变量。这允许两个变量引用相同的内容。 `&`运算符放在要引用的变量之前。
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示例：
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```
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<?php
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$var1 = "foo";
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$var2 = "bar";
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myTest($var1, $var2);
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echo $var1; //Output foo
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echo $var2; //Output BAR
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function myTest($var1, &$var2){
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$var1 = "FOO";
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$var2 = "BAR";
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}
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?>
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```
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要动态设置变量名，我们使用变量变量。当需要创建多个变量时，这可能特别有用。
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示例：
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```
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<?php
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$var = 'Tom';
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echo $var; //Output Tom
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$$var = 'Cat'; //The value of $$var is the value of $var. So $$var and $Tom give the same output.
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echo $$var; //Output Cat
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echo $Tom; //Output Cat
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?>
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```
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# 可变范围
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变量的范围是指变量可访问的位置。
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* 全局范围用于在函数外声明的变量。这些变量可以从任何地方访问，但不能在函数内访问。
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* 本地范围是在函数内声明的变量，无法从函数外部的任何位置访问。
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例：
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```
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<?php
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$global = "Hello";
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function Test(){
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$local = "World";
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echo $global; //Error
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echo $local; //Output World
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}
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Test();
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echo $global; //Output Hello
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echo $local; //Error
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?>
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```
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要访问函数内的全局变量：
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```
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<?php
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$global = "Hello";
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function Test(){
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global $global;
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$local = "World";
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echo $global; //Output Hello
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echo $local; //Output World
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}
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Test();
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echo $global; //Output Hello
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echo $local; //Error
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?>
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```
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# 静态变量
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每次创建函数时，都会删除其所有局部变量。为了保留变量的最后一个值，我们将其声明为`static` 。
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示例：
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```
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<?php
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function WithStatic(){
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static $var = 0;
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echo $var;
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$var++;
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}
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WithStatic(); //Output 0
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WithStatic(); //Output 1
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WithStatic(); //Output 2
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function WithoutStatic(){
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$var = 0;
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echo $var;
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$var++;
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}
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WithoutStatic(); //Output 0
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WithoutStatic(); //Output 0
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WithoutStatic(); //Output 0
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?>
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``` |