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每天进步一点点：UTF-8 (BOM)导致的问题 by oflyhigh

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cn · @oflyhigh ·
$34.95
每天进步一点点：UTF-8 (BOM)导致的问题
之前发帖子说[正式启用eztk.net域名，见证人列表工具移至网站根目录](https://steemit.com/cn/@oflyhigh/eztk-net)，但是这个站点目前只有一个[Witness List](https://www.eztk.net/witnesses.php)，所以我实在不知道主页该写点啥。

![](https://steemitimages.com/DQmRkLq6rRew3mHfx4vYGWyqpC8wSebLPeC2iZCXAdpuGkR/image.png)
(图源 ：[pixabay](https://pixabay.com/))


既然没啥写的，就先跳转到[Witness List](https://www.eztk.net/witnesses.php)，其实跳转的方法有好多种，比如用Apache的`URL_REWRITE`或者用HTML代码`<meta http-equiv="refresh" content="5;url=https://www.eztk.net/witnesses.php"> `或者用JavaScripte的`window.location.href='https://www.eztk.net/witnesses.php;`

不过我最喜欢用的还是如下代码：
>`<?php`
`header('Location: https://www.eztk.net/witnesses.php');`
`?>`

编辑index.php，填上上述代码，保存并上传到服务器，访问，然后美滋滋地等跳转，结果一片空白，并没有跳转至我要的页面，这是咋回事呢？

查看了一下`error_log`发现了如下内容：
>`[30-Oct-2018 02:44:49 UTC] PHP Warning:  Cannot modify header information - headers already sent by (output started at /home/user/public_html/index.php:1) in /home/user/public_html/index.php on line 2`

哦，原来是这个问题啊，这个问题几十年前刚学PHP的时候我遇到无数次了，不过是在`header()`之前有了其它输出嘛(字符啊、空格之类的），去掉就好了。结果我瞪大眼睛找了半天，也没找到任何字符。

会是什么原因呢？我冥思苦想，想了好久终于灵光一现，我该不会手贱把PHP文件格式设置成了`UTF-8 (BOM)`了吧？

点击另存为，看了一下当前的文件格式，果不其然是`UTF-8 (BOM)`
>![](https://cdn.steemitimages.com/DQmXyjLyTWZ1LuLuj8jXGV682CbRoMYx9j9sSKg2xts8bFb/image.png)

而`UTF-8 `和`UTF-8 (BOM)`文件格式有啥区别呢？我们来对比一下两个文件的二进制码就知道了

![](https://cdn.steemitimages.com/DQmVus28gb3quKVB4WDj1MfxsyCfSU3hHKXcDQknYvcf7LB/image.png)

![](https://cdn.steemitimages.com/DQmYkK3Tw4Z45Zi6K5C3w3MsBvVefyySxnewiPMiEWXSk8x/image.png)

经过对比我们发现，后者比前者多出来三个字节***`0xEF,0xBB,0xBF`***，这就是导致***`Cannot modify header information - headers already sent by`***的罪魁祸首啦。

那么解决起来也很简单了，把文件另存为`UTF-8 `，就搞定啦。

有关更多关于BOM的细节，去参考[Byte order mark](https://en.wikipedia.org/wiki/Byte_order_mark)吧，我就不献丑啦。

# 相关链接

* [Byte order mark](https://en.wikipedia.org/wiki/Byte_order_mark)
* [Witness List by @oflyhigh](https://www.eztk.net/witnesses.php)
* [温故而知新：复习一下字符编码(ASCII、GB2312、Unicode、UTF-8、区位码)](https://steemit.com/encoding/@oflyhigh/ascii-gb2312-unicode-utf-8)
* [纸上得来终觉浅：来验证一下编码的问题](https://steemit.com/encoding/@oflyhigh/hydbr)
* [每天进步一点点：VC中不同编码间字符串转换](https://steemit.com/encoding/@oflyhigh/vc)

----
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@ilovecoding · 
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@julian2013 ·
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题图用了无数次了……
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@crypto.talk ·
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哈哈这个叫做branding

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@oflyhigh · 
机智👍
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@sunai ·
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码农的事儿真是不懂呀

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