void Classname::operator()(){ .... } 的作用是什么？

发布于 2024-12-08 07:19:03 字数 148 浏览 0 评论 0原文

我正在研究一些 C++ 代码，并遇到以下内容，

void Classname::operator()()
{   
    //other code here
}

我认为这与重载构造函数有关，但有人可以详细说明吗？

原文

Im working my way through some C++ code and came across the following

void Classname::operator()()
{   
    //other code here
}

I assume this has something to do with overloading the constructor, but can someone elaborate on that?

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似梦非梦 2024-12-15 07:19:03

operator() 是函数调用运算符。它允许您像函数一样使用类实例：

Classname instance;
instance(); //Will call the overload of operator() that takes no parameters.

这对于函子和各种其他 C++ 技术很有用。您本质上可以传递一个“函数对象”。这只是一个具有 operator() 重载的对象。因此，您将其传递给函数模板，然后函数模板像调用函数一样调用它。例如，如果定义了Classname::operator()(int)：

std::vector<int> someIntegers;
//Fill in list.
Classname instance;
std::for_each(someIntegers.begin(), someIntegers.end(), instance);

这将调用instance的operator()(int)成员对于列表中的每个整数。您可以在 instance 对象中拥有成员变量，以便 operator()(int) 可以执行您需要的任何处理。这比传递原始函数更灵活，因为这些成员变量是非全局数据。

operator() is the function-call operator. It allows you to use a class instance like a function:

Classname instance;
instance(); //Will call the overload of operator() that takes no parameters.

This is useful for functors and various other C++ techniques. You can essentially pass a "function object". This is just an object that has an overload of operator(). So you pass it to a function template, who then calls it like it were a function. For example, if Classname::operator()(int) is defined:

std::vector<int> someIntegers;
//Fill in list.
Classname instance;
std::for_each(someIntegers.begin(), someIntegers.end(), instance);

This will call instance's operator()(int) member for each integer in the list. You can have member variables in the instance object, so that operator()(int) can do whatever processing you require. This is more flexible than passing a raw function, since these member variables are non-global data.

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帅冕 2024-12-15 07:19:03

它使您的类成为一个称为“函子”的对象...它通常用作闭包类型对象，以便在该对象中嵌入一个状态，然后调用该对象，就好像它是一个函数一样，但是一个函数具有“状态性”，而没有全局可访问静态变量的缺点，就像尝试使用内部静态变量管理“状态”的传统 C 函数一样。

例如，

void Classname::operator()()
{   
    //other code here
}

Classname 的实例可以像 class_name_instance() 一样调用，并且其行为类似于不带参数的 void 函数。

It makes your class an object called a "Functor" ... it's often used as a closure-type object in order to embed a state with the object, and then call the object as-if it were a function, but a function that has "state-ness" without the downside of globally accessible static variables like you would have with traditional C-functions that attempt to manage a "state" with internal static variables.

For instance, with

void Classname::operator()()
{   
    //other code here
}

An instance of Classname can be called like class_name_instance(), and will behave like a void function that takes no arguments.

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难如初 2024-12-15 07:19:03

它不是重载构造函数——而是重载函数调用运算符。如果您为类定义了 this，那么您可以调用该类的实例，就好像它是一个函数一样。这样的对象通常称为函子。

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∞琼窗梦回ˉ 2024-12-15 07:19:03

这是重载运算符“()”的代码，它基本上允许您将类用作不带参数的函数，您还可以有类似的内容：

SomeOtherClass Classname::operator ()(Argument1 a, Argument2 b, *[etc]*); and use it like:
Classname instance;
SomeOtherClass someother =  instance(arg1, arg2);

有关重载的更多信息，您可以检查：
Operators_in_C_and_C++

That's the code to overload the operator '()' which basically allows you to use the class as a function with no parameters, you could also have something like:

SomeOtherClass Classname::operator ()(Argument1 a, Argument2 b, *[etc]*); and use it like:
Classname instance;
SomeOtherClass someother =  instance(arg1, arg2);

For more info on overloading you can check:
Operators_in_C_and_C++

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