blocks|key|3472446|text|您可以做的是将您的方法创建为静态方法。它将产生与用类名为您的方法命名空间相同的效果。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3472447|class+Vector
{
public:
++++float+x_;
++++float+y_;
++++float+z_;

++++Vector(float+x,+float+y,+float+z)+:+x_(x),+y_(y),+z_(z)+{}
++++static+float+scalar(Vector+a,+Vector+b);
};|code-block|syntax|javascript|3472448|您可以在主目录中调用以下方式：|3472449|int+main()
{
++Vector+a+=+Vector(1,2,3);
++Vector+b+=+Vector(4,5,6);

++float+result+=+Vector::scalar(a,+b);
++return+0;
}|3472450|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

What you can do is create your method as a static method. It would have the same effect as namespacing your method with the class name.

<pre><code>class Vector
{
public:
 float x_;
 float y_;
 float z_;

 Vector(float x, float y, float z) : x_(x), y_(y), z_(z) {}
 static float scalar(Vector a, Vector b);
};
</code></pre>

Which you can call the following way in your main:

<pre><code>int main()
{
 Vector a = Vector(1,2,3);
 Vector b = Vector(4,5,6);

 float result = Vector::scalar(a, b);
 return 0;
}
</code></pre>

blocks|key|2422501|text|您需要将标量定义为静态，并将其称为静态方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2422502|class+Vector
{
++++...

++++static+float+scalar(Vector+a,+Vector+b);
};|code-block|syntax|javascript|2422503|和|2422504|auto+result+=+Vector::scalar(a,b);|2422505|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

You need to define scalar as static and call it as a static method:

<pre><code>class Vector
{
 ...

 static float scalar(Vector a, Vector b);
};
</code></pre>

and 

<pre><code>auto result = Vector::scalar(a,b);
</code></pre>

blocks|key|2422522|text|与其他语言不同，C%2B%2B允许您拥有非类成员的函数。您可以在向量之外定义函数，然后在没有对象前缀的情况下调用它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2422523|class+Vector
{
public:
++++float+x_;
++++float+y_;
++++float+z_;

++++Vector(float+x,+float+y,+float+z)+:+x_(x),+y_(y),+z_(z)+{}
};

float+scalar(Vector+a,+Vector+b)
{
++return+a.x_+*+b.x_+%2B+a.y_+*+b.y_+%2B+a.z_+*+b.z_;
}

int+main()
{
++Vector+a(1,2,3);
++Vector+b(4,5,6);

++float+result+=+scalar(a,+b);

++return+0;
}|code-block|syntax|javascript|2422524|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Unlike some other languages, C++ lets you have functions that are not members of a class. You can just define the function outside the Vector, and then call it without an object prefix.

<pre><code>class Vector
{
public:
 float x_;
 float y_;
 float z_;

 Vector(float x, float y, float z) : x_(x), y_(y), z_(z) {}
};

float scalar(Vector a, Vector b)
{
 return a.x_ * b.x_ + a.y_ * b.y_ + a.z_ * b.z_;
}

int main()
{
 Vector a(1,2,3);
 Vector b(4,5,6);

 float result = scalar(a, b);

 return 0;
}
</code></pre>

blocks|key|3713086|text|怎么样?|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3713087|float+Vector::scalar(const+Vector&+other)
{
++return+x_+*+other.x_+%2B+y_+*+other.y_+%2B+z_+*+other.z_;
}

int+main()
{
++Vector+a(1,2,3);
++Vector+b(4,5,6);

++float+result+=+a.scalar(b);

++return+0;
}|code-block|syntax|javascript|3713088|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

How about?

<pre><code>float Vector::scalar(const Vector&amp; other)
{
 return x_ * other.x_ + y_ * other.y_ + z_ * other.z_;
}

int main()
{
 Vector a(1,2,3);
 Vector b(4,5,6);

 float result = a.scalar(b);

 return 0;
}
</code></pre>

blocks|key|2422604|text|你们关系很亲密..。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2422605|因为ctor和dtor是“琐碎的”，所以您可以简单地实例化一个虚拟向量，并使用该虚拟标量方法。|2422606|但是，如果您不能降低(+ctor+/+dtor)的成本，或者您知道您将逐步增加它们的行为，那么您也可以使用已经存在的方法向量：：标量()对本地数据没有任何作用。因此，不需要“静态”。不需要更改代码。|offset|length|style|BOLD|2422607|int+main()
{
++Vector+a+=+Vector(1,2,3);
++Vector+b+=+Vector(4,5,6);

++//+instantiate+a+dumy+vector
++float+result1+=+Vector(0,+0,+0).scalar(a,b);++//+dummy+Vector

++//+use+an+existing+vector
++float+result2+=+a.scalar(a,b);++//+method+scalar+does+not+modify+self.

++std::cout+<<+"\n\n++"+<<+result1+<<+"++"+<<+result2+<<+std::endl;

++return+0;
}|code-block|syntax|javascript|2422608|这两个结果是相同的，即32|2422609|entityMap^0|0|0|1M|9|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|U|8|@$F|V|G|W|H|I]]|9|@]|A|$]]|$1|J|3|K|5|L|7|X|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

You are trivially close ... 

Since the ctor and dtor are 'trivial', you can simply instantiate a dummy Vector, and use that dummy's scalar method.

But if you can't bring yourself to trivialize the cost (of the ctor / dtor) or you know you will be incrementally growing their behaviour, you can also make use of either of the already existing Vector's. Note that the method Vector::scalar() does nothing to the local data. Thus, no 'static' required. No code changes required.

<pre><code>int main()
{
 Vector a = Vector(1,2,3);
 Vector b = Vector(4,5,6);

 // instantiate a dumy vector
 float result1 = Vector(0, 0, 0).scalar(a,b); // dummy Vector

 // use an existing vector
 float result2 = a.scalar(a,b); // method scalar does not modify self.

 std::cout &lt;&lt; "\n\n " &lt;&lt; result1 &lt;&lt; " " &lt;&lt; result2 &lt;&lt; std::endl;

 return 0;
}
</code></pre>

Both results are same, i.e. 32

blocks|key|2422654|text|我的第一个答案提供了两个避免更改类代码的选择。基本原理:大多数专业程序员参与的一项活动(“分配的”)是：(+a)添加功能；(+b)响应需求的变化。当然，编码错误有“修正”之处。如果将对现有代码的影响降到最低，您的工作将更小(从而更早完成，从而更好地接受)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2422655|这个答案建议在现有的类向量中添加2行，|2422656|添加默认的ctor+(注意-默认的ctor和dtor什么都不做)|ordered-list-item|2422657|添加运算符()|2422658|这两个1行添加允许您使用类作为函子。|2422659|来自Google，C%2B%2B函子：|2422660|函子(或函数对象)是一个类似于函数的C%2B%2B类。函子使用相同的旧函数调用语法进行调用。为了创建函子，我们创建了一个重载操作符()的对象。
C%2B%2B+-+GeeksforGeeks+https://www.geeksforgeeks.org/functors-in-cpp/中的函子|blockquote|offset|length|2422661|class+Vector
{
public:

+++//+...+as+above


+++//+functor+style+access:
+++Vector()+=+default;+++++++++++++++++++//+default+ctor
+++float+operator()(Vector+a,+Vector+b)+{+return+scalar(a,b);+}+//+operator()

};+//+class+Vector|code-block|syntax|javascript|2422662|如何调用标量()方法？|2422663|通过函子：|2422664|int+main()
{
++Vector+a+=+Vector(1,2,3);
++Vector+b+=+Vector(4,5,6);

++float+result+=+Vector()(a,b);

++std::cout+<<+"\n\n++"+<<+result+
++++++++++++<<+++"++++++even+more+convenient:+"+<<+Vector()(a,+b)+<<+std::endl;

++return+0;
}|2422665|entityMap|0|LINK|mutability|MUTABLE|url|https://www.geeksforgeeks.org/functors-in-cpp/^0|0|0|0|0|0|0|2G|1A|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1B|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1C|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|1D|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|1E|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1F|8|@]|9|@]|A|$]]|$1|M|3|N|5|O|7|1G|8|@]|9|@$P|1H|Q|1I|1|1J]]|A|$]]|$1|R|3|S|5|T|7|1K|8|@]|9|@]|A|$U|V]]|$1|W|3|X|5|O|7|1L|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|1M|8|@]|9|@]|A|$]]|$1|10|3|11|5|T|7|1N|8|@]|9|@]|A|$U|V]]|$1|12|3|-4|5|6|7|1O|8|@]|9|@]|A|$]]]|13|$14|$5|15|16|17|A|$18|19]]]]

My first answer provided 2 choices that avoided changing any of the class code you have. Rationale: An activity that most professional programmers get involved with (ahem, 'assigned'), is a) adding functionality, and b) responding to a change in requirements. And of course, there is c) the 'fix' to coding errors. Your efforts will be smaller (and thus sooner complete, and thus better received) if you minimize impact to existing code. 

This answer suggests adding 2 lines to your existing class Vector,

<ol>
<li>add the default ctor (Note - the default ctor and dtor do nothing)</li>
<li>add operator() </li>
</ol>

These two 1 liner additions allow you to use the class as a functor. 

From Google, C++ functor:

<blockquote>
 A functor (or function object) is a C++ class that acts like a
 function. Functors are called using the same old function call syntax.
 To create a functor, we create a object that overloads the operator().
 
 Functors in C++ - GeeksforGeeks
 <a href="https://www.geeksforgeeks.org/functors-in-cpp/" rel="nofollow noreferrer">https://www.geeksforgeeks.org/functors-in-cpp/</a>
</blockquote>

<hr>

<pre><code>class Vector
{
public:

 // ... as above


 // functor style access:
 Vector() = default; // default ctor
 float operator()(Vector a, Vector b) { return scalar(a,b); } // operator()

}; // class Vector
</code></pre>

<blockquote>
 how to call the scalar() method? 
</blockquote>

Through the functor:

<pre><code>int main()
{
 Vector a = Vector(1,2,3);
 Vector b = Vector(4,5,6);

 float result = Vector()(a,b);

 std::cout &lt;&lt; "\n\n " &lt;&lt; result 
 &lt;&lt; " even more convenient: " &lt;&lt; Vector()(a, b) &lt;&lt; std::endl;

 return 0;
}
</code></pre>

I have the following class:

<pre><code>class Vector
{
public:
 float x_;
 float y_;
 float z_;

 Vector(float x, float y, float z) : x_(x), y_(y), z_(z) {}
 float scalar(Vector a, Vector b);
};
</code></pre>

and the following method:

<pre><code>float Vector::scalar(Vector a, Vector b)
{
 return a.x_ * b.x_ + a.y_ * b.y_ + a.z_ * b.z_;
}
</code></pre>

now I am initializing <code>Vector a</code> and <code>Vector b</code> in main function:

<pre><code>int main()
{
 Vector a = Vector(1,2,3);
 Vector b = Vector(4,5,6);

 float result;
 // how can I call the scalar() method and save the return value in result

 return 0;
}
</code></pre>

But now I am wondering how to call the scalar() method. I've tried to declare scalar() static but it did not work.

c++ : how can I call a method in main function without creating an object

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。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

我有以下课程：class Vector{public:    float x_;    float y_;    float z_;    Vector(float x, float y, float z) : x_(x), y_(y), z_(z) {}    float scalar(Vector a, Vecto...

问c++：如何在不创建对象的情况下调用主函数中的方法
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问c++：如何在不创建对象的情况下调用主函数中的方法EN