PHP编程中有哪些常见的低级错误？

回复内容：

• isset
  

<span class="x">$a = null;</span>
<span class="x">var_dump(isset($a)); //false</span>

涉及金钱时，使用浮点数进行计算，然后每月结算时会发现会有几块钱的偏差，但对账时却发现不了问题。

其实应该使用Integer来处理的。

更新，原来可以用bcmath库来专门解决这个问题，推荐https://packagist.org/packages/webit/bcmath 都怪我打字太快。。。

$result = $this->select();
return $reuslt;

重复造轮子。比如PHP有提供函数来实现某个功能的，但是因为自己不知道，所以自己又写了一个函数出来实现相同的功能，不但浪费时间而且增加了代码的复杂度。

1. 明文存取用户密码
   
2. 硬编码并版本控制后台系统的口令
3. 不加密cookie
4. "SELECT * FROM users where id='{$_GET['uid']}'"
5. 自己DDOS自己 foreach ($uids as $uid) { $service = ..connect...; $service ... }
6. if (条件满足 ) { ... } 没else，两个月后发现神秘bug
7. if流，if () { if () { if () { ... } } if () {} }，不反向判断简化代码
8. 在一个view里算半天逻辑输出一小段html
9. 为传参方便设计Class
10. 把SESSION当NOSQL数据库用, $_SESSION["post"]['title'] = ....
11. $data流，$data = .. if (..) $data, $data, $data ... 一路$data
12. 把Class当名字空间来用，method就是套了Class的function
13. 这样 $a->b['c']['d']['e'] ... 还不用isset
14. 把base64当加密算法
15. throw exception但懒得catch，以至于错误信息出现在http响应里让用户去catch

没加分号 我来，我来这个问题亲身经历
曾经给客户上一个模板的时候，这个模板的错误让我无言以对
贴代码

<span class="cp"><?</span>
<span class="k">echo</span> <span class="s2">"</div></span><span class="se">\r\n\t\t</span><span class="s2"></div></span><span class="se">\r\n\t</span><span class="s2"></div></span><span class="se">\r\n\t\r\n\t</span><span class="s2">"</span><span class="p">;</span>
<span class="k">if</span> <span class="p">(</span> <span class="nv">$sourceurl</span> <span class="o">!=</span> <span class="s2">"-1"</span> <span class="o">&&</span> <span class="nv">$sourceurl</span> <span class="o">!=</span> <span class="s2">""</span> <span class="o">&&</span> <span class="nv">$sourceurl</span> <span class="o">!=</span> <span class="s2">"0"</span> <span class="o">&&</span> <span class="nb">strstr</span><span class="p">(</span> <span class="nv">$sourceurl</span><span class="p">,</span> <span class="s2">"/"</span> <span class="p">)</span> <span class="p">)</span>
<span class="p">{</span>
		<span class="nv">$SourceArr</span> <span class="o">=</span> <span class="nb">explode</span><span class="p">(</span> <span class="s2">"/"</span><span class="p">,</span> <span class="nv">$sourceurl</span> <span class="p">);</span>
		<span class="nv">$sourcename</span> <span class="o">=</span> <span class="nv">$SourceArr</span><span class="p">[</span><span class="mi">1</span><span class="p">];</span>
		<span class="nv">$sourcefolder</span> <span class="o">=</span> <span class="nv">$SourceArr</span><span class="p">[</span><span class="mi">0</span><span class="p">];</span>
		<span class="k">echo</span> <span class="s2">"</span><span class="se">\t</span><span class="s2"><div id=</span><span class="se">\"</span><span class="s2">setsource</span><span class="se">\"</span><span class="s2"> class=</span><span class="se">\"</span><span class="s2">pluszone</span><span class="se">\"</span><span class="s2">>"</span><span class="p">;</span>
		<span class="k">echo</span> <span class="nv">$strPlusZone4</span><span class="p">;</span>
		<span class="k">echo</span> <span class="s2">"</div></span><span class="se">\r\n\t</span><span class="s2"><div id=</span><span class="se">\"</span><span class="s2">s_setsource</span><span class="se">\"</span><span class="s2">  class=</span><span class="se">\"</span><span class="s2">pluszonex</span><span class="se">\"</span><span class="s2">></span><span class="se">\r\n\t</span><span class="s2"><div id=</span><span class="se">\"</span><span class="s2">sourcezone</span><span class="se">\"</span><span class="s2">></div></span><span class="se">\r\n\t</span><span class="s2"></div></span><span class="se">\r\n\t</span><span class="s2">"</span><span class="p">;</span>
		<span class="k">echo</span> <span class="s2">"<s"</span><span class="p">;</span>
		<span class="k">echo</span> <span class="s2">"cript></span><span class="se">\r\n\t\$</span><span class="s2">(document).ready(function(){\r</span><span class="se">\n\t\t\$</span><span class="s2">().getPicSource();</span><span class="se">\r\n\t</span><span class="s2">});</span><span class="se">\r\n\t</span><span class="s2"></script></span><span class="se">\r\n\t</span><span class="s2">"</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">echo</span> <span class="s2">"</span><span class="se">\t</span><span class="s2"><input name=</span><span class="se">\"</span><span class="s2">sourcename</span><span class="se">\"</span><span class="s2"> type=</span><span class="se">\"</span><span class="s2">hidden</span><span class="se">\"</span><span class="s2"> id=</span><span class="se">\"</span><span class="s2">sourcename</span><span class="se">\"</span><span class="s2"> value=</span><span class="se">\"</span><span class="s2">"</span><span class="p">;</span>
<span class="k">echo</span> <span class="nv">$sourcename</span><span class="p">;</span>
<span class="k">echo</span> <span class="s2">"</span><span class="se">\"</span><span class="s2"> size=</span><span class="se">\"</span><span class="s2">35</span><span class="se">\"</span><span class="s2"> /></span><span class="se">\r\n\t</span><span class="s2"><input name=</span><span class="se">\"</span><span class="s2">sourcefolder</span><span class="se">\"</span><span class="s2"> type=</span><span class="se">\"</span><span class="s2">hidden</span><span class="se">\"</span><span class="s2"> id=</span><span class="se">\"</span><span class="s2">sourcefolder</span><span class="se">\"</span><span class="s2"> value=</span><span class="se">\"</span><span class="s2">"</span><span class="p">;</span>
<span class="k">echo</span> <span class="nv">$sourcefolder</span><span class="p">;</span>