C# 大端与小端
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<div class="tit" style="font-family: Arial; font-size: 14px; line-height: 26px">c# 通信中字节序处理。</div>
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<p>原文地址：https://blog.csdn.net/ybhjx/article/details/50475440<p\>
</p\></p><p>
最近在写一个短信下发功能，客户端使用c#和java的短信网关的进行网络通信。</p>
<p>
之前使用java进行开发，一切正常，改用c#无法收到网关应答。</p>
<p>
想了半天意识到是不是网络字节序问题，</p>
<p>
<span style="font-size: 18px">java默认就是大端字节序，和网络字节序是一至的，所以不转换也不会有问题，</span></p>
<p>
而c#在windows平台上是小端字节序。</p>
<p>
网络发送字节流是按大端序发送，也就是从左到右发送，和c#的小端序相反，造成网关不能正常识别协议。</p>
<p>
尝试c#中转换一下字节序，通信成功。</p>
<p>
c#中字节序转换有两种方法。</p>
<p>
非字串使用 System.BitConverter.GetBytes()方法，先读入字节数组中，然后再用Array.Reverse()对byte数组反序一下，得到大端序字节数组。</p>
<p>
代码： </p>
<p>
short x = 6;</p>
<p>
byte[] a=System.BitConverter.GetBytes(x); //得到小端字节序数组</p>
<p>
Array.Reverse(a); //反转数组转成大端。</p>
<p>
</p>
<p>
</p>
<p>
另外c#直接提供了网络字节序转换方法。</p>
<p>
System.Net.IPAddress.HostToNetworkOrder（本机到网络转换）</p>
<p>
System.Net.IPAddress.NetworkToHostOrder(网络字节转成本机)</p>
<p>
推荐使用这种方法，简单有效。</p>
<p>
代码示例：</p>
<p>
short x = 6;</p>
<p>
short b = System.Net.IPAddress.HostToNetworkOrder(x); //把x转成相应的大端字节数</p>
<p>
byte[] bb = System.BitConverter.GetBytes(b); //这样直接取到的就是大端字节序字节数组。</p>
<p>
</p>
<p>
对于字符串型：使用 System.Text.Encoding.Default.GetBytes();直接取字串对应字节数组。</p>
<p>
不知道为什么这个方法取到的直接就是大端字节数组。不用转换。</p>
<p>
后来查了一下，关于字串的字节序问题，因为gbk和utf-8都是以单个字节表示数字的，所以不存在字节序问题，在多个不同系统架构都用。对于utf-16，则是以双字节表示一个整数，所以为会有字节序问题，分大小端unicode。</p>
<p>
System.Text.Encoding.Default.GetBytes();在我的简体中文系统上是以gb2312的编码，也就是单个字来进行编码的，所以也不会有字节序问题。</p>
<p>
补充：“对于任何字符编码，编码单元的顺序是由编码方案指定的，与endian无关。例如GBK的编码单元是字节，用两个字节表示一个汉字。这两个字节的顺序是固定的，不受CPU字节序的影响。UTF-16的编码单元是word（双字节），word之间的顺序是编码方案指定的，word内部的字节排列才会受到endian的影响。”，所以utf-8也没有字节序的问题。字节序问题之存在于需要使用两个字节以上来表示整数。而UTF-8只是一串字节流，不存在字节序问题，不过将这些字节流翻译成Unicode比其他的传输方式复杂。以字节为单位编码的，无论一个汉字是多少个字节，都无字节序问题。<br>
你注意，字节序问题不是指多个字节传输的先后，这个是固定的无异议的。而是指一个多字节编码在机器中的表示方式问题。<br>
char str[] = "abaksdkakskasklasflk"；这个无字节序问题。<br>
但<br>
int str[] = {0x11223344, 2, 3 }就有字节序问题了。因为str同样数值不同机器中表示不同。</p>
<p>
而剩下的， 就是字符编码内部的字节序了。比如UTF-16是用两个字节表示一个字符，但是这两个字节内部如何排序，系统并不知道，所以必须指定字节序。但是UTF-8由于几个字节表示并不相同，一定要从那个表示长度的字节开始读，相当于一开始就知道该从哪里是队头队尾，所以不存在字节序问题。</p>
<p>
附上字节序说明：</p>
<p>
</p>
<p>
为什么要注意字节序的问题呢？你可能这么问。当然，如果你写的程序只在单机环境下面运行，并且不和别人的程序打交道，那么你完全可以忽略字节序的存在。但是，如果你的程序要跟别人的程序产生交互呢？尤其是当你把你在微机上运算的结果运用到计算机群上去的话。在这里我想说说两种语言。C/C++语言编写的程序里数据存储顺序是跟编译平台所在的CPU相关的，而JAVA编写的程序则唯一采用big endian方式来存储数据。试想，如果你用C/C++语言在x86平台下编写的程序跟别人的JAVA程序互通时会产生什么结果？就拿上面的 0x12345678来说，你的程序传递给别人的一个数据，将指向0x12345678的指针传给了JAVA程序，由于JAVA采取big
endian方式存储数据，很自然的它会将你的数据翻译为0x78563412。什么？竟然变成另外一个数字了？是的，就是这种后果。因此，在你的C程序传给JAVA程序之前有必要进行字节序的转换工作。</p>
<p>
</p>
<p>
用文字说明可能比较抽象，下面用图像加以说明。比如数字0x12345678在两种不同字节序CPU中的存储顺序如下所示：</p>
<div style="line-height: 14px; overflow: hidden"></div>
<p>
Big Endian</p>
<div style="line-height: 14px; overflow: hidden"></div>
<p>
低地址 高地址</p>
<div style="line-height: 14px; overflow: hidden"></div>
<p>
-----------------------------------------></p>
<div style="line-height: 14px; overflow: hidden"></div>
<p>
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</p>
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<p>
| 12 | 34 | 56 | 78 |</p>
<div style="line-height: 14px; overflow: hidden"></div>
<p>
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</p>
<div style="line-height: 14px; overflow: hidden"></div>
<p>
Little Endian</p>
<div style="line-height: 14px; overflow: hidden"></div>
<p>
低地址 高地址</p>
<div style="line-height: 14px; overflow: hidden"></div>
<p>
-----------------------------------------></p>
<div style="line-height: 14px; overflow: hidden"></div>
<p>
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</p>
<div style="line-height: 14px; overflow: hidden"></div>
<p>
| 78 | 56 | 34 | 12 |</p>
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<p>
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</p>
<p>
<br></p>
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<br></p>
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</p><div class="table-box"><table border="0" cellpadding="0" cellspacing="0" class="syntaxhighlighter csharp" style="border-spacing: 0; font-family: Monaco, Menlo, Consolas, "Courier New", monospace; width: 674px; color: rgba(51, 51, 51, 1); border: 1px solid rgba(204, 204, 204, 1) !important; line-height: 1.1em !important; overflow: auto !important; vertical-align: baseline !important; font-size: 13px !important; background: none rgba(245, 245, 245, 1) !important"><tbody style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"><tr style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"><td class="code" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; width: 630px; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; font-size: 13px !important; background: none !important">
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<code class="csharp keyword" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; font-weight: 700 !important; color: rgba(255, 120, 0, 1) !important; background: none !important">using</code> <code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">System.Linq;</code></div>
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<code class="csharp keyword" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; font-weight: 700 !important; color: rgba(255, 120, 0, 1) !important; background: none !important">using</code> <code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">System.Text;</code></div>
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<code class="csharp keyword" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; font-weight: 700 !important; color: rgba(255, 120, 0, 1) !important; background: none !important">using</code> <code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">System.Net;</code></div>
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<div class="line number8 index7 alt1" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
<code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">{</code></div>
<div class="line number9 index8 alt2" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
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<div class="line number10 index9 alt1" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
<code class="csharp spaces" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"> </code><code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">{</code></div>
<div class="line number11 index10 alt2" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
<code class="csharp spaces" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"> </code><code class="csharp keyword" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; font-weight: 700 !important; color: rgba(255, 120, 0, 1) !important; background: none !important">static</code> <code class="csharp keyword" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; font-weight: 700 !important; color: rgba(255, 120, 0, 1) !important; background: none !important">void</code> <code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">Main(</code><code class="csharp keyword" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; font-weight: 700 !important; color: rgba(255, 120, 0, 1) !important; background: none !important">string</code><code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">[] args)</code></div>
<div class="line number12 index11 alt1" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
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<div class="line number13 index12 alt2" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
<code class="csharp spaces" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"> </code><code class="csharp keyword" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; font-weight: 700 !important; color: rgba(255, 120, 0, 1) !important; background: none !important">byte</code><code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">[] b = { 1, 2, 3, 4 };</code></div>
<div class="line number14 index13 alt1" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
<code class="csharp spaces" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"> </code> </div>
<div class="line number15 index14 alt2" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
<code class="csharp spaces" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"> </code><code class="csharp comments" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 130, 0, 1) !important; background: none !important">//x1是小端模式值：x1=67305985=0x04030201</code></div>
<div class="line number16 index15 alt1" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
<code class="csharp spaces" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"> </code><code class="csharp keyword" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; font-weight: 700 !important; color: rgba(255, 120, 0, 1) !important; background: none !important">int</code> <code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">x1 = BitConverter.ToInt32(b, 0);</code></div>
<div class="line number17 index16 alt2" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
</div>
<div class="line number18 index17 alt1" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
<code class="csharp spaces" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"> </code><code class="csharp comments" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 130, 0, 1) !important; background: none !important">//x2是大端模式值：x2=16909060=0x01020304</code></div>
<div class="line number19 index18 alt2" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
<code class="csharp spaces" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"> </code><code class="csharp keyword" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; font-weight: 700 !important; color: rgba(255, 120, 0, 1) !important; background: none !important">int</code> <code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">x2 = IPAddress.NetworkToHostOrder(x1);</code></div>
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<code class="csharp spaces" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"> </code><code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">}</code></div>
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<code class="csharp spaces" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important"> </code><code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">}</code></div>
<div class="line number22 index21 alt1" style="border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; background: none !important">
<code class="csharp plain" style="font-family: Monaco, Menlo, Consolas, "Courier New", monospace; border: 0 !important; line-height: 1.1em !important; overflow: visible !important; vertical-align: baseline !important; color: rgba(0, 0, 0, 1) !important; background: none !important">}</code></div>
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上面代码利用IPAddress.NetworkToHostOrder( )方法实现大、小端转换。</p>
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来源：https://www.cnblogs.com/dawenxi0/p/11580420.html
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