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? php教程 php手冊(cè) PHP ?? ??(2)-php ??

PHP ?? ??(2)-php ??

Aug 18, 2016 am 08:57 AM

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php? ??? ?? ?? ??? ? ?????. ??? ?? ???? ??? ?? ? ??? ?? ??? ?????. ??: 

<span style="color: #000000">php
</span><span style="color: #800080">$x</span><span style="color: #000000">;
</span><span style="color: #0000ff">echo</span> <span style="color: #800080">$x</span><span style="color: #000000">;
</span>?>

?? ????? ??? ?? ?? ???? ?????.

PHP ?? ??(2)-php ??

? ??? Python? ????. Python?? ??? ?? ???? ??? ?????? ?? ?? ???? ????? ??? ?????.

PHP ?? ??(2)-php ????, ??? ??? ?? ???? ?? ??? ???????????

PHP? ?? ??? ?????. ??? ??? ? ??? ??? ??? ??? ????. PHP? ??? ?? ?? ???? ??? ??? ??? ???? ?????. ?? ?? ??? ??: 

<span style="color: #000000">php
</span><span style="color: #800080">$x</span>=3<span style="color: #000000">;
</span><span style="color: #800080">$y</span>=3.0<span style="color: #000000">;
</span><span style="color: #800080">$str</span>="hello"<span style="color: #000000">;
</span><span style="color: #800080">$bool</span>=<span style="color: #0000ff">false</span><span style="color: #000000">;
</span><span style="color: #800080">$arr</span>=<span style="color: #0000ff">array</span>(PHP ?? ??(2)-php ??,2,3<span style="color: #000000">);
</span><span style="color: #800080">$_null</span>=<span style="color: #0000ff">NULL</span><span style="color: #000000">;

</span><span style="color: #0000ff">echo</span> <span style="color: #008080">gettype</span>(<span style="color: #800080">$x</span>),"<br>";     <span style="color: #008000">//</span><span style="color: #008000">輸出類型為integ</span>
<span style="color: #0000ff">echo</span> <span style="color: #008080">gettype</span>(<span style="color: #800080">$y</span>),"<br>";     <span style="color: #008000">//</span><span style="color: #008000">輸出類型為double</span>
<span style="color: #0000ff">echo</span> <span style="color: #008080">gettype</span>(<span style="color: #800080">$str</span>),"<br>";   <span style="color: #008000">//</span><span style="color: #008000">輸出類型為string</span>
<span style="color: #0000ff">echo</span> <span style="color: #008080">gettype</span>(<span style="color: #800080">$bool</span>),"<br>";  <span style="color: #008000">//</span><span style="color: #008000">輸出類型為boolean</span>
<span style="color: #0000ff">echo</span> <span style="color: #008080">gettype</span>(<span style="color: #800080">$arr</span>),"<br>";   <span style="color: #008000">//</span><span style="color: #008000">輸出類型為array</span>
<span style="color: #0000ff">echo</span> <span style="color: #008080">gettype</span>(<span style="color: #800080">$_null</span>),"<br>";  <span style="color: #008000">//</span><span style="color: #008000">輸出類型為NULL</span>
?>

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PHP ?? ??(2)-php ??

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  • ??
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(PHP ?? ??(2)-php ??) ?? ? ??? ??

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?: 

<span style="color: #000000">php
</span><span style="color: #008000">/*</span><span style="color: #008000">局部作用域與全局作用域</span><span style="color: #008000">*/</span>
<span style="color: #800080">$a</span>=5<span style="color: #000000">;

</span><span style="color: #0000ff">function</span><span style="color: #000000"> test()
{
    </span><span style="color: #800080">$b</span>=PHP ?? ??(2)-php ??0<span style="color: #000000">;
    </span><span style="color: #0000ff">echo</span> "測(cè)試函數(shù)內(nèi)變量<br>"<span style="color: #000000">;
    </span><span style="color: #0000ff">echo</span> "變量a的值為：<span style="color: #800080">$a</span> <br>";  <span style="color: #008000">//</span><span style="color: #008000">變量$a未在函數(shù)內(nèi)定義，在引用時(shí)出現(xiàn)錯(cuò)誤.</span>
    <span style="color: #0000ff">echo</span> "變量b的值為:<span style="color: #800080">$b</span><br>"<span style="color: #000000">;
}

test();

</span><span style="color: #0000ff">echo</span> "測(cè)試函數(shù)外變量<br>"<span style="color: #000000">;
</span><span style="color: #0000ff">echo</span> "變量a的值為：<span style="color: #800080">$a</span> <br>"<span style="color: #000000">;
</span><span style="color: #0000ff">echo</span> "變量b的值為:<span style="color: #800080">$b</span><br>";    <span style="color: #008000">//</span><span style="color: #008000">變量$a未在函數(shù)內(nèi)定義，在引用時(shí)出現(xiàn)警告.</span>
?>

結(jié)果如下：

PHP ?? ??(2)-php ??

圖、局部變量與全局變量

可見，在局部函數(shù)里面，是不能直接訪問全局變量的，如果要訪問全局變量，須在函數(shù)里面的變量前加上global關(guān)鍵字。同樣，在函數(shù)外也不能直接訪問函數(shù)里面的變量，函數(shù)執(zhí)行結(jié)束內(nèi)存會(huì)自動(dòng)回收，故我們無法訪問到。

（2）global關(guān)鍵字

????? global 關(guān)鍵字用于函數(shù)內(nèi)訪問全局變量，在函數(shù)內(nèi)調(diào)用函數(shù)外定義的全局變量，需要用global關(guān)鍵字。值得一提的是，這和參數(shù)的調(diào)用不同，參數(shù)的調(diào)用并不會(huì)改變?cè)撟兞吭趦?nèi)存中的值，而global調(diào)用是直接調(diào)用內(nèi)存中的該值，直接對(duì)它進(jìn)行操作，故會(huì)改變其值。

<span style="color: #000000">php
</span><span style="color: #008000">/*</span><span style="color: #008000">在函數(shù)內(nèi)調(diào)用函數(shù)外的變量，需要用到global關(guān)鍵字</span><span style="color: #008000">*/</span>
<span style="color: #008000">/*重要：</span><span style="color: #008000">這種調(diào)用會(huì)改變變量在內(nèi)存中的值</span><span style="color: #008000">*/</span>
<span style="color: #800080">$x</span>=5<span style="color: #000000">;
</span><span style="color: #800080">$y</span>=6<span style="color: #000000">;
</span><span style="color: #008000">/*</span><span style="color: #008000">
 * 以下這種方式是不被允許的，只有在函數(shù)內(nèi)調(diào)用函數(shù)外的變量才能使用global
golbal $z=7;
</span><span style="color: #008000">*/</span>
<span style="color: #0000ff">function</span><span style="color: #000000"> myTest()
{
    </span><span style="color: #0000ff">global</span> <span style="color: #800080">$x</span>,<span style="color: #800080">$y</span><span style="color: #000000">;
    </span><span style="color: #800080">$y</span>=<span style="color: #800080">$x</span>+<span style="color: #800080">$y</span><span style="color: #000000">;
}

myTest();
</span><span style="color: #0000ff">echo</span> "y=<span style="color: #800080">$y</span>"  <span style="color: #008000">//</span><span style="color: #008000">輸出y=PHP ?? ??(2)-php ??PHP ?? ??(2)-php ??</span>
?>

?

*注意：超級(jí)全局變量 $GLOBALS[index]

????? php將所有全局變量存儲(chǔ)在一個(gè)名為：$GLOBALS[index]的數(shù)組中，這個(gè)數(shù)組可以在函數(shù)內(nèi)訪問，也可以用來直接更新全局變量（只能在函數(shù)內(nèi)進(jìn)行）。

實(shí)例:

<span style="color: #000000">php
</span><span style="color: #008000">/*</span><span style="color: #008000"> GLOBALS[index]的用法講解 </span><span style="color: #008000">*/</span>
<span style="color: #800080">$x</span>=5<span style="color: #000000">;
</span><span style="color: #800080">$y</span>=6<span style="color: #000000">;

</span><span style="color: #0000ff">function</span><span style="color: #000000"> myTest_PHP ?? ??(2)-php ??()
{
    </span><span style="color: #800080">$GLOBALS</span>['y']=<span style="color: #800080">$GLOBALS</span>['x']+<span style="color: #800080">$GLOBALS</span>['y'<span style="color: #000000">];
    </span><span style="color: #008000">/*</span><span style="color: #008000">index不用寫$字符，否則報(bào)錯(cuò)：$x,$y undefined
    $GLOBALS['$y']=$GLOBALS['$x']+$GLOBALS['$y'];
    </span><span style="color: #008000">*/</span><span style="color: #000000">
}

</span><span style="color: #0000ff">function</span><span style="color: #000000"> myTest_2()
{
    </span><span style="color: #800080">$GLOBALS</span>['x']=PHP ?? ??(2)-php ??5<span style="color: #000000">;
}

</span><span style="color: #0000ff">echo</span> "執(zhí)行myTest_PHP ?? ??(2)-php ??:<br>"<span style="color: #000000">;
myTest_PHP ?? ??(2)-php ??();
</span><span style="color: #0000ff">echo</span> "y=<span style="color: #800080">$y</span>","<br>"<span style="color: #000000">;
</span><span style="color: #0000ff">echo</span> "x=<span style="color: #800080">$x</span>","<br>"<span style="color: #000000">;
</span><span style="color: #800080">$GLOBALS</span>['$x']=PHP ?? ??(2)-php ??2;     <span style="color: #008000">//</span><span style="color: #008000">未將GLOBALS[index]放在函數(shù)里面，無效</span>
<span style="color: #0000ff">echo</span> "x=<span style="color: #800080">$x</span>","<br>"<span style="color: #000000">;

</span><span style="color: #0000ff">echo</span> "執(zhí)行myTest_2:<br>"<span style="color: #000000">;
myTest_2();
</span><span style="color: #0000ff">echo</span> "x=<span style="color: #800080">$x</span>","<br>"<span style="color: #000000">;
</span>?>

結(jié)果為：

GLOBALS[index] introduce

圖、GLOBALS[index]的用法示例

（3）static關(guān)鍵字

????? 在一個(gè)函數(shù)執(zhí)行完成之后，它的變量通常都會(huì)刪除，有時(shí)我們希望函數(shù)中的某個(gè)變量保留，這時(shí)我們可以在申明變量時(shí)使用static關(guān)鍵字：

實(shí)例：

<span style="color: #000000">php
</span><span style="color: #008000">/*</span><span style="color: #008000">靜態(tài)變量static的用法</span><span style="color: #008000">*/</span>
<span style="color: #0000ff">function</span><span style="color: #000000"> myTest()
{
    </span><span style="color: #0000ff">static</span> <span style="color: #800080">$x</span>=0,<span style="color: #800080">$y</span>=PHP ?? ??(2)-php ??<span style="color: #000000">;
    </span><span style="color: #0000ff">echo</span> <span style="color: #800080">$x</span><span style="color: #000000">;
    </span><span style="color: #800080">$x</span>++<span style="color: #000000">;
}

myTest(); </span><span style="color: #008000">//</span><span style="color: #008000">輸出為:0</span>
myTest(); <span style="color: #008000">//</span><span style="color: #008000">輸出為:PHP ?? ??(2)-php ??</span>
myTest(); <span style="color: #008000">//</span><span style="color: #008000">輸出為:2</span>

<span style="color: #008000">/*</span><span style="color: #008000">函數(shù)里面的靜態(tài)變量不能直接被訪問</span><span style="color: #008000">*/</span>
<span style="color: #0000ff">echo</span> <span style="color: #800080">$y</span>;  <span style="color: #008000">//</span><span style="color: #008000">輸出為：Notice: Undefined variable: y</span>
?>

（4）參數(shù)作用域

????? 參數(shù)（parameter）的作用是將值傳遞給函數(shù)的局部變量。

實(shí)例：

<span style="color: #000000">php
</span><span style="color: #008000">/*</span><span style="color: #008000">參數(shù)（parameter）傳遞</span><span style="color: #008000">*/</span>
<span style="color: #0000ff">function</span> myTest(<span style="color: #800080">$x</span><span style="color: #000000">)
{
    </span><span style="color: #0000ff">echo</span> "傳遞的值為：<span style="color: #800080">$x</span>.<br>"<span style="color: #000000">;
}

myTest(</span>5);  <span style="color: #008000">//</span><span style="color: #008000">結(jié)果為:傳遞的值為5.</span>
myTest("string") <span style="color: #008000">//</span><span style="color: #008000">結(jié)果為:傳遞的值為string.</span>
?>

?

?

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Technorati 標(biāo)簽: php,變量,local,global,static,參數(shù)傳遞,GLOBALS[index]
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