C++如何在DLL中存储程序的初始状态/识别未初始化的变量
我正在用 C++ 编写一个 DLL，以便与 VB6 一起使用。因此，我无法在 DLL 中调用构造函数（根据 此讨论< /a>）。但是，我需要在内部维护类的实例 - 因此我打算将对象保留为全局变量并从全局函数调用构造函数，然后使用另一个全局函数调用该对象的方法。
我的想法是，也许一个函数就足够了：它将检查全局变量中是否存在实例，如果不存在，则创建它，然后调用对象上的方法（或者，如果存在，则立即调用方法。）
现在，我怎样才能知道实例是否已经创建？我不能在声明中为全局变量分配任何值，对吧？据我了解，它们在 C++ 中也没有保证的默认值。
因此我的问题是：这是否可能以及如何实现？
或者我可以使用 BOOL APIENTRY DllMain( HMODULE hModule, DWORD ul_reason_for_call, LPVOID lp保留 ) 函数初始化变量？如果是这样，有人可以告诉我 ul_reason_for_call 情况到底是什么，以及当 VB6 加载 DLL 时自动调用其中哪一个，如我的链接示例中所示？
I'm writing a DLL in C++ for use with VB6. As such, I cannot have a constructor called in my DLL (according to this discussion). However, I need to maintain an instance of a class internally -- so I intend to keep the object as a global variable and call the constructor from a global function, and after that, use another global function to call a method on the object.
I had the idea that maybe one function would be enough: It would check if an instance is present in a global variable, and if not, create it, and then call the method on the object (or, if it is present, immediately call the method.)
Now, how can I find out whether an instance is already created? I can't assign a global variable any value in the declaration, right? And they also don't have a guaranteed default value in C++, as far as I understand.
Therefore my question: Is this possible anyway and how?
Or can I use the BOOL APIENTRY DllMain( HMODULE hModule, function to initialize variables? If so, can someone fill me in on what the
DWORD ul_reason_for_call,
LPVOID lpReserved
)ul_reason_for_call cases exactly are and which of these is automatically called when VB6 loads the DLL as in my linked example?
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您可以在 CPP 文件中使用全局静态变量或文件范围变量：
这些赋值语句将在 DllMain 内部调用，稍后您可以测试它们是否已正确初始化。
您可以将指针声明为 auto_ptr（如果您使用 stl 或等效的东西），以便在退出时调用析构函数。
You can use global static variables or file scope variables in your CPP files:
These assignment statements will be called inside
DllMain, later you can test if they have been initialized properly.You could declare the pointers as
auto_ptr(if you use stl or something equivalent), to have the destructors called on exit.假设您希望可以全局访问
MyClass的实例。您可以拥有一个带有静态成员的类，您的全局函数将访问该类：
...然后您的全局方法将调用 GlobalHelper::GetInstance()->Whatever() 来完成其工作。
Suppose you want an instance of
MyClassto be acessible globally.You can have a class with a static member which your global functions will access:
...and then your global methods would be calling
GlobalHelper::GetInstance()->Whatever()to do their work.您甚至不需要函数：
my_global_thingy将在程序启动时、DllMain 执行之前实例化。You don't even need a function:
my_global_thingywill be instantiated at program startup, before DllMain is executed.