blocks|key|925225|text|你是说就像|type|unstyled|depth|inlineStyleRanges|entityRanges|data|925226|#define+SET(x)+(CallMe(x))|offset|length|style|CODE|925227|ps+-关于使用预处理器的常见免责声明|925228|entityMap^0|0|0|Q|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

You mean like

<code>#define SET(x) (CallMe(x))</code>

ps - usual disclaimer about using the preprocessor

blocks|key|4592090|text|这应该通过重载各种逻辑运算符的类来完成，以创建抽象语法树，而不是实际执行操作。然后，您可以将各种SQL表达式表示为C%2B%2B代码，并获得抽象语法树，然后可以将其序列化为SQL+WHERE子句。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4592091|这并不是很难，如果你小心的话，它将是非常有效的。这比尝试使用预处理器hackery创建SQL表达式构建器要好得多。|4592092|entityMap^0|2E|5|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|N|8|@]|D|@]|E|$]]]|I|$]]

This should be done with classes that overload the various logical operators to create an abstract syntax tree instead of actually performing the operation. Then you can express various SQL expressions as C++ code and get an abstract syntax tree out which can then be serialized into an SQL <code>WHERE</code> clause.

This isn't very hard, and if you are careful about it, it will be pretty efficient. It's much better than trying to use preprocessor hackery to create an SQL expression builder.

blocks|key|2992616|text|为了得到你想要的东西，你必须把你的代码写成SET(COLUMN(price)"=hi")。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2992617|不能为内置类型重载operator=()。这样做是为了维护理智，以及其他原因。|2992618|C%2B%2B重载并不允许您强制编译器分析不同的语言。|2992619|附注:在Table类中重载operator=()仅处理Table位于=左侧的情况。这将要求COLUMN(x)返回一个Table对象，这可能不是您想要的。您可以使用adaptor类来实现此效果，但是COLUMN(x)的语法不包括此列来自哪个表，因此您也陷入了困境。|2992620|一种解决方案是这样的：|2992621|class+ColumnSetter
{public:
++++ColumnSetter(const+char*+name):+name(name),+value(0)+{}
++++ColumnSetter&+operator=(const+char*+value_)+{+value+=+value_;+}
++++operator+std::string+const+&()+const+{+std::string+result(name);
++++++++if(value)+{+result.append('=');+result.append(value);+}+return+result;+}
private:
++++const+char*+name;
++++const+char*+value;
};

#define+COLUMN(x)+ColumnSetter(#x)

void+callMe(const+std::string&+param);|code-block|syntax|javascript|2992622|根据您拥有的任何编码标准重新格式化和反内联。|2992623|entityMap^0|L|N|0|9|B|0|0|4|5|D|B|R|5|Y|1|19|9|1M|5|2Q|9|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@$9|10|A|11|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|12|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|L|3|M|5|6|7|1I|8|@]|D|@]|E|$]]|$1|N|3|O|5|P|7|1J|8|@]|D|@]|E|$Q|R]]|$1|S|3|T|5|6|7|1K|8|@]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1L|8|@]|D|@]|E|$]]]|V|$]]

To get what you want, you would have to write your code as <code>SET(COLUMN(price)"=hi")</code>.

You can't overload <code>operator=()</code> for a built-in type. This is done for sanity maintenance, among other reasons.

C++ overloading is not intended to allow you to force the compiler to parse a different language.

P.S. Overloading <code>operator=()</code> in the <code>Table</code> class only handles the case where a <code>Table</code> is on the left-hand side of the <code>=</code>. That would require <code>COLUMN(x)</code> to return a <code>Table</code> object, probably not what you want. You could use an adaptor class to get this effect, but the syntax of <code>COLUMN(x)</code> doesn't include which table this column is from, so you're stuck there too.

One way out there solution would look something like this:

<pre><code>class ColumnSetter
{public:
 ColumnSetter(const char* name): name(name), value(0) {}
 ColumnSetter&amp; operator=(const char* value_) { value = value_; }
 operator std::string const &amp;() const { std::string result(name);
 if(value) { result.append('='); result.append(value); } return result; }
private:
 const char* name;
 const char* value;
};

#define COLUMN(x) ColumnSetter(#x)

void callMe(const std::string&amp; param);
</code></pre>

Reformat and de-inline to whatever coding standards you have.

blocks|key|925335|text|这对你有好处吗？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|925336|#define+SECOND_PASS(x)+callMe(#x)
#define+COLUMN(x)+x
#define+SET(x)+SECOND_PASS(x)|code-block|syntax|javascript|925337|这会导致：|925338|callMe("price=\"hi\"");|925339|这实际上是让预处理器在转换为字符串之前删除列。|925340|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Is this any good to you?

<pre><code>#define SECOND_PASS(x) callMe(#x)
#define COLUMN(x) x
#define SET(x) SECOND_PASS(x)
</code></pre>

which results in:

<pre><code>callMe("price=\"hi\"");
</code></pre>

This essentially gets the preprocessor to remove COLUMN before converting to a string.

I have the following problem:

Let's consider we have 

<pre><code>#define SET callMe
#define COLUMN(x) #x
</code></pre>

and in our main block of our program we have the following line:
<code>SET(COLUMN(price)="hi");</code> which after the preprocessor running is translated to:

<pre><code>#callMe("price"="hi"); 
</code></pre>

I need function <code>callMe</code> signature to be <code>callMe(string str)</code> so that leaves us to have to make something to make the <code>"price"="hi"</code> to <code>"price=hi"</code> and let <code>callMe</code> function to handle the rest of the problem. Last thing to state is that all this program I describe is a part of a Table class.

The only option I have is overload the operator <code>=</code> so the <code>"price"="hi"</code> translated to the wanted one, but I can't get what I should overload because I first thought that doing the following overload 

<code>#std::string operator=(std::string str)</code> as a member function of the Table class but it seems I can't get it right on track.

Any clues of how I can achieve the wanted operations?

C++ preprocessor and overloading issues

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有以下问题：让我们考虑一下我们有#define SET callMe#define COLUMN(x) #x在我们程序的主要代码块中，我们有以下代码行：SET(COLUMN(price)="hi");，在预处理器运行后，它被转换为：#callMe("price"="hi"); 我需要函数callMe签名为callMe...

问C++预处理器和重载问题
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