c++ 类中对象计数的静态变量？
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Static variable for object count in c++ classes?
提问by mowwwalker
I would like to have a static member variable keep track of the amount of objects that have been made. Like so:
我想有一个静态成员变量来跟踪已创建的对象数量。像这样：
class test{
static int count = 0;
public:
test(){
count++;
}
}
That doesn't work because, according to VC++, a member with an in-class initializer must be constant. So I looked around and apparently you're supposed to do:
这并不工作，因为，根据VC ++， a member with an in-class initializer must be constant。所以我环顾四周，显然你应该这样做：
test::count = 0;
Which would be great, but I want count to be private.
这会很棒，但我希望 count 是私密的。
edit:Oh boy, I just realized I need to do:
编辑：哦，男孩，我刚刚意识到我需要做：
int test::count = 0;
I had seen something just do test::count = 0, so I assumed you wouldn't have to declare type again.
我已经看到了一些 just do test::count = 0，所以我认为你不必再次声明类型。
I'd like to know if there's a way to do this inside the class though.
我想知道是否有办法在课堂上做到这一点。
edit2:
编辑2：
What I'm using:
我在用什么：
class test{
private:
static int count;
public:
int getCount(){
return count;
}
test(){
count++;
}
}
int test::count=0;
Now it's saying: 'test' followed by 'int' is illegal (did you forget a ';'?)
现在它说： 'test' followed by 'int' is illegal (did you forget a ';'?)
edit3:
编辑3：
Yup, forgot a semicolon after the class definition. I'm not used to having to do that.
是的，忘记了类定义后的分号。我不习惯这样做。
回答by Seth Carnegie
Put
放
static int count;
In your header in the class definition, and
在类定义的标题中，以及
int test::count = 0;
In the .cpp file. It will still be private (if you leave the declaration in the header in the private section of the class).
在 .cpp 文件中。它仍然是私有的（如果您在类的私有部分的标题中保留声明）。
The reason you need this is because static int countis a variable declaration, but you need the definition in a single source file so that the linker knows what memory location you're referring to when you use the name test::count.
您需要它的原因是因为它static int count是一个变量声明，但您需要在单个源文件中进行定义，以便链接器知道您在使用 name 时所指的内存位置test::count。
回答by elxala
Initialization of static variable within a function is allowed so a solution can be something like this
允许在函数内初始化静态变量，因此解决方案可以是这样的
class test
{
private:
static int & getCount ()
{
static int theCount = 0;
return theCount;
}
public:
int totalCount ()
{
return getCount ();
}
test()
{
getCount () ++;
}
};
in general using this technique it is possible to work around the C++ limitation regarding static member initialization in the declaration.
一般来说，使用这种技术可以解决 C++ 关于声明中静态成员初始化的限制。
回答by Ben Voigt
staticclass members must be defined (and potentially initialized) at namespace scope, member access rules do not apply.
static类成员必须在命名空间范围内定义（并可能初始化），成员访问规则不适用。
