PHP开发实战权威指南，php实战指南_PHP教程

php中文网

发布时间：2016-07-13 10:17:12

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来源于php中文网

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PHP开发实战权威指南，php实战指南

3.2.1 变量的声明与命名

<span> 1</span> <?<span>php
</span><span> 2</span>     <span>$title</span>="hello";   <span>//</span><span>正确</span>
<span> 3</span>     <span>$title123</span>="hello";  <span>//</span><span>正确</span>
<span> 4</span>     $123title="hello";  <span>//</span><span>错误</span>
<span> 5</span>     <span>$_title</span>="hello";     <span>//</span><span>正确</span>
<span> 6</span>     $@<span>#</span><span>title="hello";   //错误</span>
<span> 7</span>     <span>$url</span>="hello";   <span>//</span><span>我们得到一个变量url</span>
<span> 8</span>     <span>echo</span> <span>$url</span>;      <span>//</span><span>结果：hello</span>
<span> 9</span>     <span>unset</span>(<span>$url</span>);   <span>//</span><span>删除一个变量url</span>
<span>10</span>     <span>echo</span> <span>$url</span>;     <span>//</span><span>结果为空</span>
<span>11</span> ?>

3.2.2 可变变量与引用赋值

<span>1</span> <?<span>php
</span><span>2</span>     <span>$var</span>="php"<span>;
</span><span>3</span>     <span>$php</span>="hello"<span>;
</span><span>4</span>     <span>echo</span> <span>$var</span>;   <span>//</span><span>输出结果php</span>
<span>5</span>     <span>echo</span> $<span>$var</span>;   <span>//</span><span>输出结果hello</span>
<span>6</span> ?>

3.3.1 字符串

<span>1</span> <?<span>php
</span><span>2</span>     <span>$title</span>="hello"<span>;  
</span><span>3</span>     <span>echo</span> '$title,world';  <span>//</span><span>结果：$title,world</span>
<span>4</span>     <span>echo</span> "<span>$title</span>,world ";  <span>//</span><span>结果：hello，world</span>
<span>5</span>     <span>echo</span> "${title},world";  <span>//</span><span>结果：hello,world</span>
<span>6</span>     <span>echo</span> "{<span>$title</span>},world";  <span>//</span><span>结果：hello,world</span>
<span>7</span>     <span>echo</span> "\$title,world";  <span>//</span><span>结果：$title,world</span>
<span>8</span> ?>

3.3.8 类型的强制转换与应用

<span>//</span><span>其他类型转换成整型</span>
<?<span>php
    </span><span>$php</span>=100.10<span>;
    </span><span>echo</span> (int)<span>$php</span>;  <span>//</span><span>输出结果：100</span>
    <span>$php</span>=<span>true</span><span>;
    </span><span>echo</span> (int)<span>$php</span>；  <span>//</span><span>输出结果：1</span>
    <span>$php</span>="123php"<span>;
    </span><span>echo</span> (int)<span>$php</span>;  <span>//</span><span>输出结果：123</span>
    <span>$php</span>="php123"<span>;  
    </span><span>echo</span> (int)<span>$php</span>;  <span>//</span><span>输出结果：0</span>
?>

<span>//</span><span>其他类型转化为字符串型</span>
<?<span>php
    </span><span>$php</span>=100.1<span>;
    </span><span>var_dump</span>((<span>string</span>)<span>$php</span>);  <span>//</span><span>输出结果：string(4)"100.1"</span>
    <span>$php</span>=<span>true</span><span>;
    </span><span>echo</span>(<span>string</span>)<span>$php</span>;  <span>//</span><span>输出结果：1</span>
?>

<span>//</span><span>其他类型转化为浮点型</span>
<?<span>php
    </span><span>$php</span>="123.2php"<span>;
    </span><span>var_dump</span>((<span>float</span>)<span>$php</span>);  <span>//</span><span>输出结果：float(123.2)</span>
    <span>$php</span>="php123.2"<span>;
    </span><span>var_dump</span>((<span>float</span>)<span>$php</span>);  <span>//</span><span>输出结果：（0）</span>
?>

<span>//</span><span>其他类型转化为布尔型</span>
<?<span>php
    </span><span>$php</span>="php"<span>;
    </span><span>var_dump</span>((bool)<span>$php</span>);  <span>//</span><span>输出结果：bool(true)</span>
    <span>$php</span>=0<span>;
    </span><span>var_dump</span>((bool)<span>$php</span>);  <span>//</span><span>输出结果：bool(false)</span>
?>