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速战速决 (1) - PHP: 概述, 常量, 变量, 运算符, 表达式, 控制语句 - webabcd

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Release： 2016-05-20 10:14:58
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速战速决 (1) - PHP: 概述, 常量, 变量, 运算符, 表达式, 控制语句



作者：webabcd


介绍
速战速决 之 PHP

  • 概述
  • 常量
  • 变量
  • 运算符
  • 表达式
  • 控制语句



示例
1、概述
basic/summary.php

<!--<span style="color: #000000;">
    PHP 概述
</span>-->

<span style="color: #000000;">php
</span><span style="color: #0000ff;">echo</span> "我在 php 开始标记和结束标记之间"<span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
</span>?>

<?php <span style="color: #0000ff;">if (<span style="color: #008080;">time</span>() % 2 == 0): ?><span style="color: #000000;">
    我是 html（用于演示 php 和 html 混编）
    </span><br>
<?php <span style="color: #0000ff;">else: ?><span style="color: #000000;">
    这里是 html（用于演示 php 和 html 混编）
    </span><br>
<?php <span style="color: #0000ff;">endif; ?>


<span style="color: #000000;">php
</span><span style="color: #0000ff;">echo</span> "可以没有 php 结束标记"<span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> "<br>";
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2、常量
basic/constant.php

<span style="color: #000000;">php
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
 * 常量
 </span><span style="color: #008000;">*/</span>

<span style="color: #008000;">//</span><span style="color: #008000;"> 用 define 来定义常量</span>
<span style="color: #008080;">define</span>("MyConst1", "MyConst1"<span style="color: #000000;">);
</span><span style="color: #0000ff;">echo</span><span style="color: #000000;"> MyConst1;
</span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

</span><span style="color: #008000;">//</span><span style="color: #008000;"> 在 PHP 5.3.0 之后支持用 const 来定义常量</span>
<span style="color: #0000ff;">const</span> MyConst2 = "MyConst2"<span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span><span style="color: #000000;"> MyConst2;
</span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;



</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
 * 魔术常量（magic constant）
 *
 * 魔术常量，在不同的场景下会有不同的值
 </span><span style="color: #008000;">*/</span>

<span style="color: #008000;">//</span><span style="color: #008000;"> __LINE__ - 文件中的当前行号, 由其在脚本中所处的行来决定</span>
<span style="color: #0000ff;">echo</span> <span style="color: #ff00ff;">__LINE__</span><span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

</span><span style="color: #008000;">//</span><span style="color: #008000;"> __FILE__ - 当前文件的完整路径和文件名，如果用在被包含文件中，则返回被包含的文件名</span>
<span style="color: #0000ff;">echo</span> <span style="color: #ff00ff;">__FILE__</span><span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

</span><span style="color: #008000;">//</span><span style="color: #008000;"> __DIR__ - 文件所在的目录,如果用在被包括文件中，则返回被包括的文件所在的目录</span>
<span style="color: #0000ff;">echo</span><span style="color: #000000;"> __DIR__;
</span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

</span><span style="color: #008000;">//</span><span style="color: #008000;"> __FUNCTION__ - 函数名称
// __CLASS__ - 类名称
// __METHOD__ - 方法名称
// __NAMESPACE__ - 命名空间名称
// __TRAIT__ - Trait 名称</span>
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3、变量
basic/variable.php

<span style="color: #000000;">php
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
 * 变量
 </span><span style="color: #008000;">*/</span>

<span style="color: #008000;">//</span><span style="color: #008000;"> 通过 $ 定义变量</span>
<span style="color: #800080;">$a</span> = "a"<span style="color: #000000;">;

</span><span style="color: #008000;">//</span><span style="color: #008000;"> 通过 $ 使用变量</span>
<span style="color: #0000ff;">echo</span> <span style="color: #800080;">$a</span>;  <span style="color: #008000;">//</span><span style="color: #008000;"> output: a</span>
<span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

</span><span style="color: #008000;">//</span><span style="color: #008000;"> 通过 $ 使用变量，即使外面加了双引号也同样会使用变量</span>
<span style="color: #0000ff;">echo</span> "<span style="color: #800080;">$a</span>"; <span style="color: #008000;">//</span><span style="color: #008000;"> output: a</span>
<span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

</span><span style="color: #008000;">//</span><span style="color: #008000;"> 通过 {} 界定变量名称，比如"$ab"，php会使用变量$ab，而实际上我们想要使用的是$a，此时就可以通过 {} 来界定变量名称，如下：</span>
<span style="color: #0000ff;">echo</span> "{<span style="color: #800080;">$a</span>}b"; <span style="color: #008000;">//</span><span style="color: #008000;"> output: ab</span>
<span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

</span><span style="color: #008000;">//</span><span style="color: #008000;"> 外面加双引号，但是不想使用变量的话，可以通过转移符“\”来将“$”变成字符串</span>
<span style="color: #0000ff;">echo</span> "\$a"; <span style="color: #008000;">//</span><span style="color: #008000;"> output: $a</span>
<span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

</span><span style="color: #008000;">//</span><span style="color: #008000;"> 外面加单引号的话就按字符串处理了</span>
<span style="color: #0000ff;">echo</span> '$a'; <span style="color: #008000;">//</span><span style="color: #008000;"> output: $a</span>
<span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;



</span><span style="color: #008000;">//</span><span style="color: #008000;"> 变量之间赋值</span>
<span style="color: #800080;">$b</span> = <span style="color: #800080;">$a</span><span style="color: #000000;">;
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 通过 & 定义引用。下面的例子是让 $c 引用 $a</span>
<span style="color: #800080;">$c</span> = &<span style="color: #800080;">$a</span><span style="color: #000000;">;
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 为 $a 重新赋值</span>
<span style="color: #800080;">$a</span> = "aa"<span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> "<span style="color: #800080;">$b</span>"; <span style="color: #008000;">//</span><span style="color: #008000;"> output: a</span>
<span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> "<span style="color: #800080;">$c</span>"; <span style="color: #008000;">//</span><span style="color: #008000;"> output: aa</span>
<span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;



</span><span style="color: #0000ff;">function</span><span style="color: #000000;"> f1()
{
    </span><span style="color: #008000;">//</span><span style="color: #008000;"> 这里的 $a 引用的是局部变量 $a，然而之前在 f1 这个局部范围内并没有定义 $a，所以你要使用 $a 的话它是不会有任何内容的</span>
    <span style="color: #0000ff;">echo</span> <span style="color: #800080;">$a</span>; <span style="color: #008000;">//</span><span style="color: #008000;"> output:</span>
    <span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
}
f1();

</span><span style="color: #0000ff;">function</span><span style="color: #000000;"> f2()
{
    </span><span style="color: #008000;">//</span><span style="color: #008000;"> 通过 global 关键字标记 $a，则在此局部范围之后，再使用 $a 时将会使用全局版本的 $a</span>
    <span style="color: #0000ff;">global</span> <span style="color: #800080;">$a</span><span style="color: #000000;">;
    </span><span style="color: #0000ff;">echo</span> <span style="color: #800080;">$a</span>; <span style="color: #008000;">//</span><span style="color: #008000;"> output: aa</span>
    <span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
}
f2();

</span><span style="color: #0000ff;">function</span><span style="color: #000000;"> f3()
{
    </span><span style="color: #008000;">//</span><span style="color: #008000;"> 通过 $GLOBALS 直接使用指定变量的全局版本</span>
    <span style="color: #0000ff;">echo</span> <span style="color: #800080;">$GLOBALS</span>['a']; <span style="color: #008000;">//</span><span style="color: #008000;"> output: aa</span>
    <span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
}
f3();

</span><span style="color: #0000ff;">function</span><span style="color: #000000;"> f4()
{
    </span><span style="color: #008000;">//</span><span style="color: #008000;"> 通过 static 来定义静态变量，其常驻内存</span>
    <span style="color: #0000ff;">static</span> <span style="color: #800080;">$i</span> = 0<span style="color: #000000;">;
    </span><span style="color: #0000ff;">echo</span> <span style="color: #800080;">$i</span><span style="color: #000000;">;
    </span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

    </span><span style="color: #800080;">$i</span>++<span style="color: #000000;">;
}
f4(); </span><span style="color: #008000;">//</span><span style="color: #008000;"> output: 0</span>
f4(); <span style="color: #008000;">//</span><span style="color: #008000;"> output: 1</span>
f4(); <span style="color: #008000;">//</span><span style="color: #008000;"> output: 2</span>


<span style="color: #800080;">$x</span> = "aaa"<span style="color: #000000;">;
</span><span style="color: #008000;">//</span><span style="color: #008000;"> variable variables（可变变量），将变量的值作为变量名
// 下面这句等同于 $aaa = "bbb";（因为 $x 的值是 aaa，所以 $$x 等同于 $aaa）</span>
$<span style="color: #800080;">$x</span> = "bbb"<span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> <span style="color: #800080;">$aaa</span>; <span style="color: #008000;">//</span><span style="color: #008000;"> output: bbb</span>
<span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> $<span style="color: #800080;">$x</span>; <span style="color: #008000;">//</span><span style="color: #008000;"> output: bbb</span>
<span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;



</span><span style="color: #800080;">$s</span> = "12345"<span style="color: #000000;">;
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 大括号的作用: 用于指示字符串变量中的单个字符（下标从 0 开始）</span>
<span style="color: #800080;">$s</span>{1} = 'x'<span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> <span style="color: #800080;">$s</span>; <span style="color: #008000;">//</span><span style="color: #008000;"> output: 1x345</span>
<span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 大括号的作用: 用于界定变量的名称（比如下面使用的变量是 $s，而不是 $ss）</span>
<span style="color: #0000ff;">echo</span> "{<span style="color: #800080;">$s</span>}s"; <span style="color: #008000;">//</span><span style="color: #008000;"> output: 1x345s</span>
<span style="color: #0000ff;">echo</span> "<br>";
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4、运算符, 表达式, 控制语句
basic/statement.php

<span style="color: #000000;">php
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
 * 运算符，表达式，控制语句
 </span><span style="color: #008000;">*/</span>

<span style="color: #008000;">//</span><span style="color: #008000;"> 运算符，表达式，控制语句和其他的语言都差不多
// 以下写一些个人认为需要强调的东西

// . 字符串运算符</span>
<span style="color: #800080;">$s1</span> = "hello "<span style="color: #000000;">;
</span><span style="color: #800080;">$s2</span> = "webabcd"<span style="color: #000000;">;
</span><span style="color: #800080;">$s3</span> = <span style="color: #800080;">$s1</span> . <span style="color: #800080;">$s2</span><span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> <span style="color: #800080;">$s3</span>; <span style="color: #008000;">//</span><span style="color: #008000;"> output: hello webabcd</span>
<span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

</span><span style="color: #800080;">$s1</span> .= "wanglei"; <span style="color: #008000;">//</span><span style="color: #008000;"> output: hello wanglei</span>
<span style="color: #0000ff;">echo</span> <span style="color: #800080;">$s1</span><span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;


</span><span style="color: #008000;">//</span><span style="color: #008000;"> == 和 === 的区别</span>
<span style="color: #800080;">$a1</span> = "1"; <span style="color: #008000;">//</span><span style="color: #008000;"> 字符串</span>
<span style="color: #800080;">$b1</span> = 1; <span style="color: #008000;">//</span><span style="color: #008000;"> 整型</span>
<span style="color: #800080;">$c1</span> = "1"; <span style="color: #008000;">//</span><span style="color: #008000;"> 字符串</span>
<span style="color: #0000ff;">if</span> (<span style="color: #800080;">$a1</span> == <span style="color: #800080;">$b1</span>) <span style="color: #008000;">//</span><span style="color: #008000;"> 两个不同类型的数据做 == 比较，系统会自动转换</span>
<span style="color: #000000;">{
    </span><span style="color: #0000ff;">echo</span> '$a1 == $b1'; <span style="color: #008000;">//</span><span style="color: #008000;"> output: $a1 == $b1</span>
    <span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
}
</span><span style="color: #0000ff;">if</span> (<span style="color: #800080;">$a1</span> === <span style="color: #800080;">$b1</span>) <span style="color: #008000;">//</span><span style="color: #008000;"> 两个不同类型的数据做 === 比较，系统不会自动转换</span>
<span style="color: #000000;">{
    </span><span style="color: #008000;">//</span><span style="color: #008000;"> 不成立</span>
<span style="color: #000000;">}
</span><span style="color: #0000ff;">if</span> (<span style="color: #800080;">$a1</span> === <span style="color: #800080;">$c1</span><span style="color: #000000;">)
{
    </span><span style="color: #0000ff;">echo</span> '$a1 === $c1'; <span style="color: #008000;">//</span><span style="color: #008000;"> output: $a1 === $c1</span>
    <span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
}


</span><span style="color: #008000;">//</span><span style="color: #008000;"> 对于 {} 方式的或者省略了 {} 方式的 if/else 语句来说，elseif 和 else if 是一样的</span>
<span style="color: #0000ff;">if</span> (1 == 2<span style="color: #000000;">)
    </span><span style="color: #0000ff;">echo</span> "1 == 2"<span style="color: #000000;">;
</span><span style="color: #0000ff;">else</span> <span style="color: #0000ff;">if</span> (1 == 1<span style="color: #000000;">)
    </span><span style="color: #0000ff;">echo</span> "1 == 1"<span style="color: #000000;">;
</span><span style="color: #0000ff;">elseif</span> (2 == 2<span style="color: #000000;">)
    </span><span style="color: #0000ff;">echo</span> "2 == 2"<span style="color: #000000;">;
</span><span style="color: #0000ff;">else</span>
    <span style="color: #0000ff;">echo</span> "else"<span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

</span><span style="color: #008000;">//</span><span style="color: #008000;"> 对于 : 方式的 if/else 语句来说，只能用 elseif 而不用能 else if</span>
<span style="color: #0000ff;">if</span> (1 == 2):
    <span style="color: #0000ff;">echo</span> "1 == 2"<span style="color: #000000;">;
</span><span style="color: #008000;">//</span><span style="color: #008000;"> else if (1 == 1):
  //  echo "1 == 1";</span>
<span style="color: #0000ff;">elseif</span> (2 == 2):
    <span style="color: #0000ff;">echo</span> "2 == 2"<span style="color: #000000;">;
</span><span style="color: #0000ff;">else</span>:
    <span style="color: #0000ff;">echo</span> "else"<span style="color: #000000;">;
</span><span style="color: #0000ff;">endif</span><span style="color: #000000;">;
</span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;


</span><span style="color: #008000;">//</span><span style="color: #008000;"> foreach 语句的用法</span>
<span style="color: #800080;">$array1</span> = <span style="color: #0000ff;">array</span>(1, 2, 3, 4<span style="color: #000000;">);
</span><span style="color: #0000ff;">foreach</span> (<span style="color: #800080;">$array1</span> <span style="color: #0000ff;">as</span> <span style="color: #800080;">$value</span><span style="color: #000000;">)
{
    </span><span style="color: #0000ff;">echo</span> <span style="color: #800080;">$value</span><span style="color: #000000;">;
    </span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
}
</span><span style="color: #0000ff;">foreach</span> (<span style="color: #800080;">$array1</span> <span style="color: #0000ff;">as</span> <span style="color: #800080;">$key</span> => <span style="color: #800080;">$value</span><span style="color: #000000;">)
{
    </span><span style="color: #0000ff;">echo</span> <span style="color: #800080;">$key</span> . " - " . <span style="color: #800080;">$value</span><span style="color: #000000;">;
    </span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
}


</span><span style="color: #008000;">//</span><span style="color: #008000;"> try catch finally 的用法</span>
<span style="color: #0000ff;">try</span><span style="color: #000000;">
{
    </span><span style="color: #0000ff;">echo</span> "try"<span style="color: #000000;">;
    </span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

    </span><span style="color: #0000ff;">throw</span> <span style="color: #0000ff;">new</span> <span style="color: #0000ff;">Exception</span>("error message", 999); <span style="color: #008000;">//</span><span style="color: #008000;"> 要想写自定义的 Exception 的话，就继承 Exception 就好</span>
<span style="color: #000000;">}
</span><span style="color: #0000ff;">catch</span> (<span style="color: #0000ff;">Exception</span> <span style="color: #800080;">$ex</span><span style="color: #000000;">)
{
    </span><span style="color: #0000ff;">echo</span> "catch"<span style="color: #000000;">;
    </span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;

    </span><span style="color: #0000ff;">echo</span> <span style="color: #008080;">sprintf</span>("message: %s, code: %d, file: %s, line: %d, trace: %s", <span style="color: #800080;">$ex</span>->getMessage(), <span style="color: #800080;">$ex</span>->getCode(), <span style="color: #800080;">$ex</span>->getFile(), <span style="color: #800080;">$ex</span>->getLine(), <span style="color: #800080;">$ex</span>-><span style="color: #000000;">getTraceAsString());
    </span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
}
finally
{
    </span><span style="color: #0000ff;">echo</span> "finally"<span style="color: #000000;">;
    </span><span style="color: #0000ff;">echo</span> "<br>"<span style="color: #000000;">;
}</span>
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