函数参数中的赋值运算符 C++ [英] assignment operator within function parameter C++

问题描述

我正在研究数据结构(列表、堆栈、队列)，这部分代码让我很困惑.

I'm studying data structures (List, Stack, Queue), and this part of code is confusing me.

ListNode( const Object& theElement = Object(), ListNode * node = NULL);


template<class Object>
ListNode<Object>::ListNode( const Object& theElement, ListNode<Object> * node) {
    element = theElement;
    next = node;
}

1. 为什么函数参数中有赋值运算符?
2. Object() 调用有什么作用?

1. Why there are assignment operators within function parameters?
2. What does Object() call do?

推荐答案

那些不是赋值运算符.这些是默认参数 为函数.

Those are not assignment operators. Those are default arguments for the function.

一个函数可以有一个或多个默认参数，这意味着如果在调用点没有提供参数，则使用默认值.

A function can have one or more default arguments, meaning that if, at the calling point, no argument is provided, the default is used.

void foo(int x = 10) { std::cout << x << std::endl; }

int main()
{
  foo(5); // will print 5
  foo(); // will print 10, because no argument was provided
}

在您发布的示例代码中，ListNode 构造函数有两个带有默认参数的参数.第一个默认参数是 Object()，它只是调用 默认构造函数，用于Object.这意味着如果没有 Object 实例被传递给 ListNode 构造函数，将使用一个默认值 Object()，这只是意味着一个默认值- 构造Object.

In the example code you posted, the ListNode constructor has two parameters with default arguments. The first default argument is Object(), which simply calls the default constructor for Object. This means that if no Object instance is passed to the ListNode constructor, a default of Object() will be used, which just means a default-constructed Object.

另见:
使用默认函数参数的优势
函数参数的默认值

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