在C＆＃x2B;＆＃x2B;中分配一般类为null
我在调整程序从C＃到C ++时遇到了麻烦。给定课程将其分配为空值是非常令人讨厌的。但是C ++不接受等效形式“ nullptr”，
class Point{
public:
int x,y;
}
//...
Point p = nullptr;
有某种方法可以解决它吗？
I am having kind of a trouble adapting a program from C# to C++. It's very commom given a class to assign it the null value. But C++ is not accepting the equivalent form 'nullptr'
class Point{
public:
int x,y;
}
//...
Point p = nullptr;
There is some way of solving it?
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您不能将
nullptr分配给类，因为类是一种类型而不是变量。通过键入点P = nullptr;您正在做什么，因为您要编译器找到point接受nullptr >。您可以通过执行此操作来创建
point作为自动变量的对象：或者简单地：
为此，您需要定义一个初始化
x和<的构造函数代码> y ，因为您尚未为成员变量提供默认值。根据该语句居住的上下文，
p将分配在堆或堆栈上。如果您在主函数中实例化p，则将是后者。您可以通过执行此操作来创建指向
Point对象的指针：但是，您只会创建一个指针。您将需要进一步照顾分配，您可以这样做：
在这种情况下，您还应在程序结束之前释放分配的内存：
You cannot assign
nullptrto a class because a class is a type and not a variable. What you're doing by typingPoint p = nullptr;is that you're asking the compiler to find a constructor ofPointwhich accepts anullptr.You can either create an object of
Pointas an automatic variable by doing this:or simply like this:
for which however you will need to define a constructor which initializes
xandybecause you haven't provided the member variables with default values.Depending on the context in which this statement resides,
pwill either be allocated on the heap or on the stack. In case you're instantiatingpin the main function, it will be the latter.You can create a pointer to an object of
Pointby doing this:However, you will only have created a pointer. You will need to further take care of allocation, which you can do like this:
in which case you should also free the allocated memory before your program ends like so:
问题是
p是您示例中的一种非分子类型。这意味着它不能用nullptr初始化。p的类型是点。您可以制作
p一个指向point的指针，以便可以使用nullptr初始化它，如下所示：或者
如果要创建一个类型的对象
point然后这样做的一种方法是：我还建议参考a 良好的C ++书为了更好地理解该概念。
The problem is that
pis a non-pointer type in your example. This means that it cannot be initialized with anullptr. The type ofpisPoint.You can make
pa pointer to aPointso that you can initialize it with anullptras shown below:Or
If you want to create an object of the class type
Pointthen one way of doing so is as follows:I would also recommend referring to a good C++ book for a better understanding of the concept.