论坛站务软件水平考试华为认证计算机等级PMP认证思科认证Photoshop3DMAX编程语言移动开发系统运维产品运营淘宝营销办公软件Ps修图云计算大数据摄影就业

<p id="toc_1" style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);"><strong style="border: 0px; margin: 0px; padding: 0px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;另类的写法有惊喜</strong></p><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;我们在阅读某些源代码的时候会发现有一种另类的写法，比如</p><p style="text-align: center"><img src="/Public/forum/ueditor/image/20170705/1499218898818226.jpg" alt="1499218898818226.jpg"/></p><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;其实这是一种很聪明的写法，它可以很大程度上杜绝手误造成的严重bug。 假如我们在正常方法中把&nbsp;<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">==</code>&nbsp;误写成&nbsp;<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">=</code>&nbsp;，那么<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">if($result = false)</code>&nbsp;就会恒定返回true，导致在实际运行中产生未知的Bug，如果使用异常的写法出现手误变成时<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">if(false = $false)</code>&nbsp;,编辑器会抛出一个error，我们就可以及时发现并修复问题。</p><h3 id="toc_2" style="border: 0px; margin: 0px 0px 20px; padding: 0px; font-size: 20px; font-stretch: normal; line-height: 30px; font-family: &quot;Microsoft YaHei&quot;, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">‘&lt;?php’开始前不要有空行，php脚本结尾的 ‘?&gt;’ 尽量省略</h3><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;假如有一个文件在&nbsp;<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">?&gt;</code>&nbsp;后有一个空白行，那么你在使用&nbsp;<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">session_start()</code>&nbsp;等方法时，会返回一个警告<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">headers already sent by xxx</code>&nbsp;，这是因为&nbsp;<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">session_start()</code>&nbsp;要求使用前不能有任何输出。 同理&nbsp;<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">&lt;?php</code>&nbsp;前的空行也会存在同样的问题。</p><h3 id="toc_3" style="border: 0px; margin: 0px 0px 20px; padding: 0px; font-size: 20px; font-stretch: normal; line-height: 30px; font-family: &quot;Microsoft YaHei&quot;, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;字符串和数字在一起时，要留神</h3><p style="text-align: center"><img src="/Public/forum/ueditor/image/20170705/1499218937234509.jpg" alt="1499218937234509.jpg"/></p><p><span style="color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;解决的方案比较简单，只要在</span><code style="border: 0px; margin: 0px; padding: 0px; font-size: 15px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">.</code><span style="color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);">连接左右加上空格就可以防止语法错误。</span></p><p style="text-align: center"><img src="/Public/forum/ueditor/image/20170705/1499218968135593.jpg" alt="1499218968135593.jpg"/></p><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;这个例子中输出true是不是让你大吃一惊，其实php中将字符串和数字做比较时，会把字符串强制转换为int性，转换规则为&nbsp;<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">如果字符串是数字开头，那么取开头数字作为转换结果，如果开头不是数字那么就为0</code></p><h3 id="toc_4" style="border: 0px; margin: 0px 0px 20px; padding: 0px; font-size: 20px; font-stretch: normal; line-height: 30px; font-family: &quot;Microsoft YaHei&quot;, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;字符串的运算，你惹不起</h3><p style="text-align: center"><img src="/Public/forum/ueditor/image/20170705/1499219093724892.jpg" alt="1499219093724892.jpg"/></p><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);">你以为会输出从a到z？那你就错了，亮瞎你的输出结果如下：</span></p><p style="text-align: center"><img src="/Public/forum/ueditor/image/20170705/1499219135316852.jpg" alt="1499219135316852.jpg"/></p><h3 style="border: 0px; margin: 0px 0px 20px; padding: 0px; font-size: 20px; font-stretch: normal; line-height: 30px; font-family: &quot;Microsoft YaHei&quot;, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;时刻小心精度丢失的情况</h3><p><span style="color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);"></span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p><p style="text-align: center"><img src="/Public/forum/ueditor/image/20170705/1499219225754979.jpg" alt="1499219225754979.jpg"/></p><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);">精度丢失的问题在其他语言中有会有，但是在PHP这种弱类型的语言中更加需要注意。</span></p>

论坛站务软件水平考试华为认证计算机等级PMP认证思科认证Photoshop3DMAX编程语言移动开发系统运维产品运营淘宝营销办公软件Ps修图云计算大数据摄影就业