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<!DOCTYPE html>
<html>
<head>
<meta content="text/html; charset=UTF-8" http-equiv="content-type">
<title>ch03-04</title>
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<body>
<div class="os1">3.4 使用 QByteArray </div>
<br>
本节学习 QByteArray 的两种用法，第一种作为字符串处理类，类似 QString ，但 QByteArray
内部字符编码不确定，所以要慎用。第二种是作为纯的字节数组，里面可以包含多个 '\0' ，经常用于网络数据的接收和发送。本节示例代码下载地址在末尾小节
3.4.5 里。<br>
<br>
<div class="os2">3.4.1 QByteArray和char</div>
<br>
Qt 最常用的字符串类是内码固定的 QString，而针对传统类似 C 语言 char* 的字符串，Qt 提供了 QByteArray
类来处理。QString 的字符单元是 QChar，QByteArray 的字节单元是 char。头文件 <QByteArray>
不仅自身以类的形式提供，它还针对传统 C 语言的字符串函数做了安全版本的封装，都加了 q 字母前缀，如
qstrlen、qstrncmp、qstrcpy，这些是全局函数，专门处理传统 C 语言的 char* 字符串，用法与 C
语言风格完全类似，比较简单，本节就不介绍了。本节主要介绍 QByteArray 类的使用。<br>
<br>
QByteArray 类可以处理以 '\0' 结尾的传统字符串，包括 UTF-8 编码和其他如 GBK、Big5
等多字节编码的字符串，在作为字符串使用时，QByteArray
内部字符编码格式是不限定的，可以是任意编码的，所以程序员自己必须要事先确定程序会用到哪些编码的 QByteArray 。因为 Qt5 源文件规定是
UTF-8 编码的，所以 QByteArray 内部使用 UTF-8 编码的字符串居多。QByteArray
在赋值、传参数、返回值时也是使用隐式共享机制提高运行效率，只有字符串发生修改时才会执行深拷贝。<br>
<br>
在文件处理、网络数据收发等场景，QByteArray 类是作为纯字节数组来使用的，里面可以包含任意数据，比如一堆
'\0'，这时不要拿它当字符串看，它的存储长度与 qstrlen 计算的长度经常不一致。对于网络数据收发，QByteArray 经常配合
QDataStream 使用，对 Qt 数据类型做串行化（Serializing）。<br>
<br>
<div class="os2">3.4.2 QByteArray作为字符串使用</div>
<br>
QByteArray 类作为字符串使用时，它会自动在字符串末尾添加 '\0' ，末尾的 '\0' 不计入字符串长度。QByteArray
字符串的内部编码是不固定的，比如前面 QString 的 toLocal8Bit 和 toUtf8 函数返回的对象全是 QByteArray
类型。QByteArray 字符串的数据来源可能有：<br>
<ul>
<li>①源代码里的字符串，这时 QByteArray 内码与源文件的编码有关，UTF-8 编码源文件生成的很可能就是 UTF-8 编码的字符串。</li>
<li>②本地文本文件，从文件读取的字符串与该文件使用的字符编码有关，Linux 上常用 UTF-8，而 Windows 经常使用 ANSI
多字节编码，简体 Windows 系统一般是 GBK，而繁体默认是 Big5。</li>
<li>③网页数据，网页本身也是文本文件，有它自己的文本编码格式，这时网页文件编码格式决定 QByteArray 字符串的编码格式。</li>
</ul>
我们这里示范的是第一种，全部用 UTF-8 编码的 QByteArray 字符串。QByteArray 类关于字符串处理的成员函数基本和 QString
类的一样，函数名和参数都是类似的。但注意因为 QByteArray 内码不确定，它没有 arg 函数，也没有字符编码转换的函数。QByteArray
关于字符串处理的函数就不枚举了，和上一节 QString 的差不多，下面直接看示例代码：<br>
<div class="code"> <span style=" color:#808000;">void</span><span style=" color:#c0c0c0;">
</span><span style=" color:#000000;">TestStr</span><span style=" color:#000000;">()</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//内码</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">UTF-8</span>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#000000;">{</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//数值与字符串转换</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#808000;">int</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">nDec</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span style=" color:#000080;">800</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basDec</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basDec</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">setNum</span><span
style=" color:#000000;">(</span><span style=" color:#000000;">nDec</span><span style=" color:#000000;">);</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//数值转字符串</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">basDec</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basReal</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;">"125.78999"</span><span style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#808000;">double</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">dblReal</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000000;">basReal</span><span style=" color:#000000;">.</span><span
style=" color:#000000;">toDouble</span><span style=" color:#000000;">();</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//字符串转数值</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span>fixed<span style=" color:#000000;"><<</span><span
style=" color:#000000;">dblReal</span><span style=" color:#000000;">;</span></pre>
<pre style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><br></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//运算符</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basABCD</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;">"ABCD"</span><span style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basXYZ</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;">"XYZ"</span><span style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<(</span><span style=" color:#000000;">basABCD</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;"><</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000000;">basXYZ</span><span style=" color:#000000;">);</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//二者字符编码一致才能比较！</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<(</span><span style=" color:#000000;">basABCD</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">==</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000000;">basXYZ</span><span style=" color:#000000;">);</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<(</span><span style=" color:#000000;">basABCD</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">>=</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basXYZ</span><span
style=" color:#000000;">);</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<(</span><span style=" color:#000000;">basABCD</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">+</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000000;">basXYZ</span><span style=" color:#000000;">);</span></pre>
<pre style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><br></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//子串处理</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basHanzi</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;">"1234打印汉字"</span><span style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//作为字符串时</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">QByteArray::length()</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">和</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;">qstrlen()</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;">一致</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">basHanzi</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">length</span><span
style=" color:#000000;">()<<</span><span style=" color:#008000;">"\t"</span><span
style=" color:#000000;"><<</span><span style=" color:#000000;">qstrlen</span><span
style=" color:#000000;">(</span><span style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basHanzi</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">data</span><span style=" color:#000000;">()</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">);</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//重复</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basMoreHanzi</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000000;">basHanzi</span><span style=" color:#000000;">.</span><span
style=" color:#000000;">repeated</span><span style=" color:#000000;">(</span><span
style=" color:#000080;">2</span><span style=" color:#000000;">);</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">basMoreHanzi</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">count</span><span
style=" color:#000000;">(</span><span style=" color:#008000;">"1234"</span><span
style=" color:#000000;">);</span><span style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//统计次数</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">basMoreHanzi</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">startsWith</span><span
style=" color:#000000;">(</span><span style=" color:#008000;">"1234"</span><span
style=" color:#000000;">);</span><span style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//开头判断</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">basMoreHanzi</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">endsWith</span><span
style=" color:#000000;">(</span><span style=" color:#008000;">"汉字"</span><span style=" color:#000000;">);</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//结尾判断</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">basMoreHanzi</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">indexOf</span><span
style=" color:#000000;">(</span><span style=" color:#008000;">"1234"</span><span
style=" color:#000000;">);</span><span style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//从左边查出现位置</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">basMoreHanzi</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">lastIndexOf</span><span
style=" color:#000000;">(</span><span style=" color:#008000;">"1234"</span><span
style=" color:#000000;">);</span><span style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//从右边查出现位置</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//替换</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basMoreHanzi</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">replace</span><span
style=" color:#000000;">(</span><span style=" color:#008000;">"1234"</span><span
style=" color:#000000;">,</span><span style=" color:#c0c0c0;"> </span><span style=" color:#008000;">"一二三四"</span><span
style=" color:#000000;">);</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">basMoreHanzi</span><span
style=" color:#000000;">;</span></pre>
<pre style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><br></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//切割字符串</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basComplexFile</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;">"</span><span style=" color:#c0c0c0;"> </span><span style=" color:#008000;">/home/user/somefile.txt</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">\t\t</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">"</span><span style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">basFileName</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000000;">basComplexFile</span><span style=" color:#000000;">.</span><span
style=" color:#000000;">trimmed</span><span style=" color:#000000;">();</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//剔除两端空白</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">basFileName</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//分隔得到新的</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">对象列表</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QList</span><span
style=" color:#000000;"><</span><span style=" color:#800080;">QByteArray</span><span
style=" color:#000000;">></span><span style=" color:#c0c0c0;"> </span><span style=" color:#000000;">baList</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000000;">basFileName</span><span style=" color:#000000;">.</span><span
style=" color:#000000;">split</span><span style=" color:#000000;">(</span><span
style=" color:#008000;">'/'</span><span style=" color:#000000;">);</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//打印</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#808000;">for</span><span
style=" color:#000000;">(</span><span style=" color:#808000;">int</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000000;">i</span><span style=" color:#000000;">=</span><span style=" color:#000080;">0</span><span
style=" color:#000000;">;</span><span style=" color:#c0c0c0;"> </span><span style=" color:#000000;">i</span><span
style=" color:#000000;"><</span><span style=" color:#000000;">baList</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">length</span><span
style=" color:#000000;">();</span><span style=" color:#c0c0c0;"> </span><span style=" color:#000000;">i</span><span
style=" color:#000000;">++)</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">{</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">i</span><span
style=" color:#000000;"><<</span><span style=" color:#008000;">"\t"</span><span
style=" color:#000000;"><<</span><span style=" color:#000000;">baList</span><span
style=" color:#000000;">[</span><span style=" color:#000000;">i</span><span style=" color:#000000;">];</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">}</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//没有段落函数</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#000000;">}</span></pre>
</div>
<br>
上面测试函数第一段是数值与字符串互相转换的，比较简单，打印结果是：<br>
<span style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">"800"</span>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">125.789990</span></p>
<br>
浮点数转换时，定点计数法和科学计数法都是可以接受的，上面示范的是定点数。这些函数声明和功能都可以查阅 QByteArray 类的帮助文档。<br>
<br>
第二段代码是运算符函数的，需要注意的是一定要在确定字符串内部字符编码的情况下，才能进行比较和拼接，上面用的全是 UTF-8
。不能将不同编码格式的字符串比较，因为得到的结果没意义，反而会造成误导。上面比较运算符的打印结果为：<br>
<span style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">true</span>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">false</span></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">false</span></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">"ABCDXYZ"</span></p>
<br>
第三段是子串查询处理的，注意只有当 QByteArray 作为字符串处理时，它的 length() 函数计算的长度才会和全局函数 qstrlen()
计算的结果一致。子串部分打印的结果为：<br>
<span style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">16
16</span>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">2</span></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">true</span></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">true</span></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">0</span></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">16</span></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">"一二三四打印汉字一二三四打印汉字" </span></p>
<br>
上面示范的 basMoreHanzi.replace("1234", "一二三四") ，这种形式的替换函数会对所有匹配的子串进行替换，它的声明是：<br>
<div class="code"> QByteArray & replace(const char *
before, const char * after)</div>
如果要对指定位置的子串替换，需要换一个声明形式的 replace 函数，比如：<br>
<div class="code"> QByteArray & replace(int pos, int
len, const char * after)</div>
这个函数会对指定位置 pos 开始的长度为 len 的子串进行替换，这个函数声明只做一次替换。<br>
对于 replace 函数，必须注意字符编码的问题，UTF-8 的英文字符占用 1 字节，汉字通常是 3
字节，这种不确定性在替换函数和其他分隔子串函数时尤其需要注意，因为 3 字节的汉字如果被截断，就成错误的字符，造成信息损失。因此尽量不要用
QByteArray 类来处理字符串，尤其是涉及分割和替换的。QString 类的字符长度是固定的，所以最适合做字符串处理。<br>
<br>
最后一段代码是子串分隔的，trimmed 函数功能也是去除两端的空白区域，split 函数将字符串分隔为多个子串之后按照
QList<QByteArray> 类型返回，QList 是一个模板类，QList<QByteArray> 就是存储多个
QByteArray 对象的列表，可以直接用中括号 [] 访问里面的各个对象。最后一段代码打印的结果如下：<br>
<span style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">"/home/user/somefile.txt"</span>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">0 ""</span></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">1 "home"</span></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">2 "user"</span></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">3 "somefile.txt"</span></p>
<br>
分隔结果与上一节 QString 是一样的，对于开头 '/' 左边没有字符的情况，一样会分出来一个空字符串对象。因为一般用 QString
来处理文本字符串，QByteArray 类没有 section 函数，所以字符串处理时优先用 QString 类。<br>
<br>
<div class="os2">3.4.3 QByteArray作为字节数组使用</div>
<br>
在读写文件、网络数据收发过程中经常将 QByteArray 作为缓冲区存储字节数据，这时候 QByteArray 就是纯的字节数组，里面可以包含任意个
'\0' 字节。下面以网络数据传输为例讲解，比如网络传输过程中既要传输数值类型 int、double，又要传输字符串类型 char*，对于普通的 C++
，最常用的是自定义一个结构体：<br>
<div class="code"><span style=" color:#808000;">struct</span><span style=" color:#c0c0c0;">
</span><span style=" color:#800080;">NetData</span>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#000000;">{</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#808000;">int</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#800000;">nVersion</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#808000;">double</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#800000;">dblValue</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#808000;">char</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#800000;">strName</span><span
style=" color:#000000;">[</span><span style=" color:#000080;">256</span><span style=" color:#000000;">];</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#000000;">};</span></pre>
</div>
发数据时就将数值赋值给结构体对象的成员变量，字符串就用 strcpy
函数塞进去。这种方式可行，但缺乏灵活性，下次如果要传个不同的数据组合，就得重新定义。<br>
Qt 对这类组合数据的打包方法就叫串行化（Serializing），在 Qt 帮助文档的索引里输入关键词 Serializing 就可以看到关于 Qt
串行化的帮助主题（Serializing Qt Data Types），除了 C++ 基本数值类型，Qt
还对大量自身的类对象做了串行化。串行化得到一个字节数组 QByteArray ，可以直接用于发送。Qt 串行化数据接收就是发送的逆过程，都是通过
QDataStream 流实现。下面简单示范一对函数，首先是串行化输出：<br>
<div class="code"><span style=" color:#800080;">QByteArray</span><span style=" color:#c0c0c0;">
</span><span style=" color:#000000;">TestSerialOut</span><span style=" color:#000000;">()</span>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#000000;">{</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//数据</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#808000;">int</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">nVersion</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000080;">1</span><span style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#808000;">double</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">dblValue</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000080;">125.78999</span><span style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QString</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">strName</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#800080;">QObject</span><span style=" color:#000000;">::</span><span
style=" color:#000000;">tr</span><span style=" color:#000000;">(</span><span style=" color:#008000;">"This</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">an</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;">example."</span><span style=" color:#000000;">);</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//字节数组保存结果</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">baResult</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//串行化的流</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QDataStream</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">dsOut</span><span
style=" color:#000000;">(&</span><span style=" color:#000000;">baResult</span><span
style=" color:#000000;">,</span><span style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QIODevice</span><span
style=" color:#000000;">::</span><span style=" color:#800080;">ReadWrite</span><span
style=" color:#000000;">);</span><span style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//做输出，构造函数用指针</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//设置Qt串行化版本</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">dsOut</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">setVersion</span><span
style=" color:#000000;">(</span><span style=" color:#800080;">QDataStream</span><span
style=" color:#000000;">::</span><span style=" color:#800080;">Qt_5_0</span><span
style=" color:#000000;">);</span><span style=" color:#008000;">//使用Qt 5.0 版本流</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//串行化输出</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">dsOut</span><span
style=" color:#000000;"><<</span><span style=" color:#000000;">nVersion</span><span
style=" color:#000000;"><<</span><span style=" color:#000000;">dblValue</span><span
style=" color:#000000;"><<</span><span style=" color:#000000;">strName</span><span
style=" color:#000000;">;</span></pre>
<pre style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><br></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//显示长度</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">baResult</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">length</span><span
style=" color:#000000;">()<<</span><span style=" color:#008000;">"\t"</span><span
style=" color:#000000;"><<</span><span style=" color:#000000;">qstrlen</span><span
style=" color:#000000;">(</span><span style=" color:#000000;">baResult</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">data</span><span style=" color:#000000;">());</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//返回对象</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#808000;">return</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">baResult</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#000000;">}</span></pre>
</div>
该函数里给定了三个数据：整数、浮点数和字符串对象，通过流 dsOut 将三个数据打包存到字节数组 baResult
里。对于串行化输出，QDataStream 的构造函数是以字节数组的指针和读写模式 QIODevice::ReadWrite 为参数，其构造函数声明为：<br>
<div class="code">QDataStream(QByteArray * a, QIODevice::OpenMode mode)</div>
然后设置串行化流的版本兼容，上面代码使用的是 Qt 5.0 版本的流格式；流格式设置好之后，就可以用 <<
将数据输出到流里面，QDataStream 类的函数会将数据打包好存到字节数组里面，最后返回这个字节数组对象就行了。<br>
以字节数组方式使用的 QByteArray 对象，它的长度是不能用 qstrlen 之类的函数计算的，上面函数打印的结果如下：<br>
<span style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">48
0</span><br>
<br>
字节数组实际占用 48 字节空间，而 qstrlen 函数计算的是 0，因为该字节数组第一个字节就是 '\0' 。<br>
该函数返回的 baResult 就包含了三个要发送的数据，baResult 里面具体的数据格式不需要关心，收发两端 setVersion
的版本号一致就可以了。使用串行化就不再需要自定义结构体，所以用起来很方便。<br>
网络收发过程到后面网络专题的学习再讲，现在仅学习一下串行化输出和输入的函数，baResult 数据的解析函数如下：<br>
<div class="code"> <span style=" color:#808000;">void</span><span style=" color:#c0c0c0;">
</span><span style=" color:#000000;">TestSerialIn</span><span style=" color:#000000;">(</span><span
style=" color:#808000;">const</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#800080;">QByteArray</span><span style=" color:#000000;">&</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">baIn</span><span
style=" color:#000000;">)</span>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#000000;">{</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//输入流</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QDataStream</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">dsIn</span><span style=" color:#000000;">(</span><span
style=" color:#000000;">baIn</span><span style=" color:#000000;">);</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//只读的流，构造函数用常量引用</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//设置Qt串行化版本</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">dsIn</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">setVersion</span><span
style=" color:#000000;">(</span><span style=" color:#800080;">QDataStream</span><span
style=" color:#000000;">::</span><span style=" color:#800080;">Qt_5_0</span><span
style=" color:#000000;">);</span><span style=" color:#008000;">//使用Qt</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">5.0</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;">版本流</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//变量</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#808000;">int</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">nVersion</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#808000;">double</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">dblValue</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QString</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">strName</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//串行化输入</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">dsIn</span><span
style=" color:#000000;">>></span><span style=" color:#000000;">nVersion</span><span
style=" color:#000000;">>></span><span style=" color:#000000;">dblValue</span><span
style=" color:#000000;">>></span><span style=" color:#000000;">strName</span><span
style=" color:#000000;">;</span></pre>
<pre style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><br></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//打印</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">nVersion</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span>fixed<span style=" color:#000000;"><<</span><span
style=" color:#000000;">dblValue</span><span style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">strName</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#000000;">}</span></pre>
</div>
对于输入流的构造，参数是常量引用，其声明如下：<br>
<div class="code">QDataStream(const QByteArray & a)</div>
这个声明是针对只读的输入流。输入流定义好之后，同样是设置流的版本号，要与输出端的一致。然后使用 >> 从输入流提取数据即可。上面函数打印的结
果如下：<br>
<span style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">1</span>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">125.789990</span></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" font-family:'Courier'; font-size:10pt; color:#aa00aa;">"This an example."</span></p>
<br>
可见与输出函数里的完全一样。对于 Qt 程序的网络通信，都可以类似上面方法对数据进行打包和解析，是比较方便的。<br>
<br>
QByteArray 有针对数据处理的一些函数，比如基 64
转换和压缩解压函数：fromBase64、toBase64、qCompress、qUncompress 等，这些函数可以到使用的时候再查帮助文档。<br>
<br>
<div class="os2">3.4.4 QByteArray和QString合理的使用方式</div>
<br>
因为 QByteArray 既可以用作字符串，又可以用作字符数组，它的使用方式比较多。而且作为字符串时，它内部的字符编码格式又是不固定的，所以
QByteArray 有诸多的不确定性。Qt 帮助文档里面明确说了，如果要做字符串方面的处理，都应当使用 QString
，除非是嵌入式系统里面内存有限，不得不用 QByteArray 的情况。对于本地化编码的字符串，可以用 QString::fromLocal8Bit
函数将字符串源转为 QString 对象；对于 UTF-8 编码的字符串，可以用 QString::fromUtf8 函数实现转换。如果要反过来转换，就
用对应的 to*** 函数。通常情况下有这些函数就够用了。<br>
<br>
对于文件读写和网络数据收发，这些一般都是用 QByteArray 对象作为输入输出缓冲区，并且可以利用 QDataStream
做串行化，将多个数据打包成 QByteArray 。通常情况下，对于纯字节数据的处理使用 QByteArray 。<br>
<br>
在有些情况下，需要 QString 和 QByteArray 对多种编码格式字符串进行转换，需要二者协作，下面给个协作的示例：<br>
<div class="code"> <span style=" color:#808000;">void</span><span style=" color:#c0c0c0;">
</span><span style=" color:#000000;">TestCooperation</span><span style=" color:#000000;">()</span>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#000000;">{</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//源字符串</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QString</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">strSrc</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#800080;">QObject</span><span style=" color:#000000;">::</span><span
style=" color:#000000;">tr</span><span style=" color:#000000;">(</span><span style=" color:#008000;">"1234abcd</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">千秋萬載</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;">壹統江湖"</span><span style=" color:#000000;">);</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//转为</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">UTF-8</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">strSrc</span><span
style=" color:#000000;">.</span><span style=" color:#000000;">toUtf8</span><span
style=" color:#000000;">();</span></pre>
<pre style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><br></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//明确地转为</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">GB18030</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QTextCodec</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">*</span><span style=" color:#000000;">codecGB</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#800080;">QTextCodec</span><span style=" color:#000000;">::</span><span
style=" color:#000000;">codecForName</span><span style=" color:#000000;">(</span><span
style=" color:#008000;">"GB18030"</span><span style=" color:#000000;">);</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">strGB</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000000;">codecGB</span><span style=" color:#000000;">-></span><span
style=" color:#000000;">fromUnicode</span><span style=" color:#000000;">(</span><span
style=" color:#000000;">strSrc</span><span style=" color:#000000;">);</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//转为GB18030</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">strGB</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">codecGB</span><span
style=" color:#000000;">-></span><span style=" color:#000000;">toUnicode</span><span
style=" color:#000000;">(</span><span style=" color:#000000;">strGB</span><span
style=" color:#000000;">);</span><span style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//转回QString</span></pre>
<pre style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><br></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//明确地转为</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">Big5</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QTextCodec</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">*</span><span style=" color:#000000;">codecBig5</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#800080;">QTextCodec</span><span style=" color:#000000;">::</span><span
style=" color:#000000;">codecForName</span><span style=" color:#000000;">(</span><span
style=" color:#008000;">"Big5"</span><span style=" color:#000000;">);</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#800080;">QByteArray</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">strBig5</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#000000;">=</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#000000;">codecBig5</span><span style=" color:#000000;">-></span><span
style=" color:#000000;">fromUnicode</span><span style=" color:#000000;">(</span><span
style=" color:#000000;">strSrc</span><span style=" color:#000000;">);</span><span
style=" color:#c0c0c0;"> </span><span style=" color:#008000;">//转为Big5</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">strBig5</span><span
style=" color:#000000;">;</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#c0c0c0;"> </span><span style=" color:#000080;">qDebug</span><span
style=" color:#000000;">()<<</span><span style=" color:#000000;">codecBig5</span><span
style=" color:#000000;">-></span><span style=" color:#000000;">toUnicode</span><span
style=" color:#000000;">(</span><span style=" color:#000000;">strBig5</span><span
style=" color:#000000;">);</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;">//转回QString</span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#000000;">}</span></pre>
</div>
除了 QString 自带的 to*** 等函数实现不同字符编码的转换，更为专业的是 QTextCodec
类，专门用于不同文本编码格式的转换。上面示例函数以源字符串 strSrc 为起点，首先实现与 GB18030 编码互相转换，然后实现与 Big5
编码互相转换。<br>
获取编码器的语法格式是：<br>
<div class="code">QTextCodec *codecGB =
QTextCodec::codecForName("GB18030");</div>
codecGB 是保存编码器的指针，静态函数 QTextCodec::codecForName 根据指定的编码名称获取相应的编码器，示例的是
"GB18030"。如果要将 QString 转成其他编码的 QByteArray，就用 fromUnicode 函数，反过来就用 toUnicode
函数。<br>
上面对 GB18030 和 Big5 都做了示范，打印的结果如下图所示：<br>
<center><img src="images/ch03/ch03-04-01.png"></center>
<br>
qDebug 打印 QString 对象和 UTF-8 字符串时汉字不会乱码，而 GB18030 和 Big5 等编码的汉字会乱码，只有数字、英文字符等
ASCII 码是正常显示的。<br>
<br>
<div class="os2">3.4.5 QByteArray示例代码</div>
<br>
本节 QByteArray 示例就是以上 4 个测试函数的合集，下载地址：<br>
<a href="https://lug.ustc.edu.cn/sites/qtguide/QtProjects/ch03/testqbytearray/testqbytearray.7z">
https://lug.ustc.edu.cn/sites/qtguide/QtProjects/ch03/testqbytearray/testqbytearray.7z
</a> <br> 下载之后解压到比如 D:\QtProjects\ch03\testqbytearray
文件夹里面，然后打开项目文件，阅读源代码。<br>
这里主要把包含的头文件和 main 函数贴出来，4 个测试函数内容不重复贴了：<br>
<div class="code"> <span style=" color:#008000;">//testqbytearray.cpp</span>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span
style=" color:#000080;">#include</span><span style=" color:#c0c0c0;"> </span><span
style=" color:#008000;"><QApplication></span></pre>
<pre style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;"><span