程序员成长记(一)：7类

最新推荐文章于 2025-06-15 11:45:38 发布

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最新推荐文章于 2025-06-15 11:45:38 发布

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本文链接：https://blog.youkuaiyun.com/u011104647/article/details/48649395

本文详细解析了C++中Sales_data类的构造函数，包括不同构造函数的使用场景及如何初始化类成员变量。同时介绍了const成员函数的意义以及隐式类型转换的规则。

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1):引入const成员函数表示this是一个指向常量的指针：P231

<span style="font-size:18px;">struct Sales_data{
   std::string isbn() const {return bookNO;}
}</span>

如果isbn是一个普通函数而且this是一个普通指针参数，则我们应该把this声明成const Sales_data *const 。在isbn函数体内部不会改变this 所指的对象，所以把this 设置为指向常量的指针有助于提高函数的灵活性。此时，紧跟在参数表后面的const表示this是一个指向常量的指针。

2):Sales_data类的代码：摘自Nick Feng的博客

练习7.37

<code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"><span style="color: inherit;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*
*练习7.37
*2015/7/15
*问题描述：练习7.37：使用本节提供的Sales_data类，确定初始化下面的变量时分别使用了哪个构造函数，然后罗列出每个对象所有数据成员的值。
Sales_data first_item（cin） //调用Sales_data(std::istream &is) 
int main()
{
 Sales_data next;   //调用Sales_data(std::string s = "")
 Sales_data last("9-999-99999-9");//调用  Sales_data(const std::string &s, unsigned n, double p)
}

*功能：弄清构造函数 
*作者：Nick Feng 
*邮箱：nickgreen23@163.com 
* 
*/</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <iostream></span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <string></span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">using</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">namespace</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> Sales_data{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span>:
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">friend</span> istream &read(istream &, Sales_data &);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//一个友元函数read,便于Sales_data类直接访问 </span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">friend</span> ostream &print(ostream &os, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> Sales_data &item);
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Sales_data() = default;//默认构造函数 </span>
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Sales_data(const std::string &s) : bookNo(s){ }</span>
    Sales_data(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">string</span> &s, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">unsigned</span> n, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> p) : bookNo(s), units_sold(n), revenue(p*n){ }
    Sales_data(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::istream &is){
        read(is,*<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);
    }

    Sales_data(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">string</span> s = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span>) : bookNo(s) {}
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Sales_data(std::istream is ) {}</span>
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//Sales_data(std::istream &is = cin)  {}</span>

    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">string</span> isbn() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> bookNo;}
    Sales_data& combine(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> Sales_data&);
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> avg_price() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span>;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span>:
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">string</span> bookNo;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">unsigned</span> units_sold = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> revenue = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0.0</span>;
};

Sales_data add(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> Sales_data&, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> Sales_data&);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::ostream &print(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::ostream&, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> Sales_data&);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::istream &read(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::istream&, Sales_data&);

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> Sales_data::avg_price() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span>{
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (units_sold)
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> revenue/units_sold;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> 
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
}

Sales_data& Sales_data::combine(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> Sales_data &rhs)
{
    units_sold += rhs.units_sold;
    revenue += rhs.revenue;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> *<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>;
}

</span><span style="color:#ff0000;"><strong>istream &read(istream &is, Sales_data &item)</strong></span><span style="color:rgba(0, 0, 0, 0);">
{
    </span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span><span style="color:rgba(0, 0, 0, 0);"> price = </span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span style="color:rgba(0, 0, 0, 0);">;
    is >> item.bookNo >> item.units_sold >> price;
    item.revenue = price * item.units_sold;
    </span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span><span style="color:rgba(0, 0, 0, 0);"> is; 
}

ostream &print(ostream &os, </span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span><span style="color:rgba(0, 0, 0, 0);"> Sales_data &item){
    os << item.isbn() << </span><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" "</span><span style="color:rgba(0, 0, 0, 0);"> << item.units_sold << </span><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" "</span><span style="color:rgba(0, 0, 0, 0);">
       << item.revenue << </span><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" "</span><span style="color:rgba(0, 0, 0, 0);"> << item.avg_price();
    </span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span><span style="color:rgba(0, 0, 0, 0);"> os;
}

Sales_data add(</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span><span style="color:rgba(0, 0, 0, 0);"> Sales_data &lhs, </span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span><span style="color:rgba(0, 0, 0, 0);"> Sales_data &rhs){
    Sales_data sum = lhs;
    sum.combine(rhs);
    </span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span><span style="color:rgba(0, 0, 0, 0);"> sum;
}

</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 
Sales_data::Sales_data(std::istream &is)
{
   <strong> read(is,*this);</strong>
}
*/</span><span style="color:rgba(0, 0, 0, 0);">

Sales_data first_item(</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">cin</span><span style="color:rgba(0, 0, 0, 0);">);
</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span><span style="color:rgba(0, 0, 0, 0);"> main()
{
   print(</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">cout</span><span style="color:rgba(0, 0, 0, 0);">,first_item);
    </span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">cout</span><span style="color:rgba(0, 0, 0, 0);"> << endl;
    Sales_data next;
     print(</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">cout</span><span style="color:rgba(0, 0, 0, 0);">,next);
    </span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">cout</span><span style="color:rgba(0, 0, 0, 0);"> << endl;
    Sales_data last(</span><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"9-999-99999-9"</span><span style="color:rgba(0, 0, 0, 0);">);
    print(</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">cout</span><span style="color:rgba(0, 0, 0, 0);">,last);
    </span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">cout</span><span style="color:rgba(0, 0, 0, 0);"> << endl;
    </span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span><span style="color:rgba(0, 0, 0, 0);"> </span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span style="color:rgba(0, 0, 0, 0);">;
 } </span></code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">关键是：输入输出流函数及其使用，如果提供cin作为接受istream&参数的构造函数的默认实参，这样的构造函数为：</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">Sales_data (std::istream & is = cin){}.</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">
</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">3):使用默认构造函数：P263</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">Sales_data obj();  //错误，声明了一个函数而非一个对象；</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">Sales_data obj;    //正确，声明了一个对象。</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">
</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">4):默认构造函数与编译器合成的默认构造函数：P262</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">默认构造函数是参数表为空的构造函数；</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">如果类没有定义默认构造函数，则编译器只能按照自己的理解合成一个默认构造函数。</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">
</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">5):隐式类类型转换：P264</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">能通过一个实参调用的构造函数（参数只能为一个）定义了一条从构造函数的参数类型向类类型隐式转换的规则。PS：只允许一步类型转换。</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">item.combine(string("9-99-999-9"));   //正确</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">item.combine(Sales_data("9-99-999-9"));  //正确</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">item.combine("9-99-999-9");   //错误</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">item.combine(cin); //从istream到Sales_data的转换。</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">抑制构造函数定义的隐式转换：</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">class Sales_data{</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"><span style="white-space:pre">	</span>explicit Sales_data(const std::string &s) : bookNo(s){}  // explicit关键字只允许出现在类的构造函数声明处</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"><span style="white-space:pre">	</span>explicit Sales_data(std::istream &);</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">}</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"> 显示强制类型转换：</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">item.combine(Sales_data(null_book));</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">item.combine(static_cast<Sales_data>(cin));</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">
</code><code class="hljs cpp has-numbering" style="display: block; padding: 0px; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-image: initial; background-attachment: initial; background-color: transparent; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">
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