创建DLL后函数指针赋值导致错误

Question

我为我的申请写了一个class。在这个 class 中有一个静态函数指针，用于通过网络套接字进行通信。在启动时，我将此函数指针分配给 class 之外的函数并且工作正常，没有任何问题。现在我从 class 创建了 DLL，但是当我将此指针分配给我的函数时，出现 "unresolved external symbol" 错误。我如何可以毫无问题地将 class 内部的静态函数指针分配给 class 外部的函数？

这是我的 class:

(header, "MyClass.h")

#define IMPORT_DLL

#ifdef IMPORT_DLL
    #define DLL_IMPORT_EXPORT __declspec(dllimport) 
#else
    #define DLL_IMPORT_EXPORT __declspec(dllexport) 
#endif

namespace nmspace
{
    class MyClass
    {
        //Constructors
        DLL_IMPORT_EXPORT MyClass();
        DLL_IMPORT_EXPORT MyClass(size_t ID);

        //Destructor
        DLL_IMPORT_EXPORT ~MyClass();

        ....

        //This static function pointer should be assigned to a function outside of class
        //this pointer used frequently
        static bool(*Class_Transmit)(uint8_t* TX_buffer, size_t TX_size, size_t Port);
    }
}

（来源，"MyClass.cpp"）

#include "MyClass.h"

bool(*MyClass::Class_Transmit)(uint8_t* TX_buffer, size_t TX_size, size_t Port) = nullptr;

//Constructor
void MyClass::MyClass()
{
    size_t Sock_num = 0
    uint8_t TX_buffer[20] = "Transmit done";
    bool is_connected = false;
    is_connected = Class_Transmit(TX_buffer, 20, Sock_num);
}

(主要, "main.cpp")

#include "MyClass.h"

bool MyFunc(uint8_t* TX_buffer, size_t TX_size, size_t Port)
{
    ....
    return true;
}

int main()
{
    HINSTANCE hinstLib;
    hinstLib = LoadLibrary(TEXT("myclass.dll"));

    // If the handle is valid, try to get the function address.
    if (hinstLib != NULL)
        return false;


    //Assign network socket function for "Class_Transmit" class for communication
    MyClass::Class_Transmit = MyFunc;
    return 0;
}

Error LNK2001 unresolved external symbol "public: static bool (__cdecl* 
nmspace::MyClass::Class_Transmit)(unsigned char *,unsigned int,unsigned int)"
 (?Class_Transmit@MyClass@nmspace@@2P6A_NPAEII@ZA)

Answer 1

该错误表明该函数需要位于 nmspace 命名空间中。请尝试以下操作：

namespace nmspace
{
    bool MyFunc(uint8_t* TX_buffer, size_t TX_size, size_t Port)
    {
        return true;
    }
}

完成之后，您需要清理其余的声明。以下完整程序编译和链接没有问题：

#include <cstdint>
#include <cstdlib>

namespace nmspace
{
    class MyClass
    {
        public:
            static bool (*Class_Transmit)(uint8_t* TX_buffer, size_t TX_size, size_t Port);
    };
}

bool (*nmspace::MyClass::Class_Transmit)(uint8_t* TX_buffer, size_t TX_size, size_t Port) = nullptr;


namespace nmspace
{
    bool MyFunc(uint8_t* TX_buffer, size_t TX_size, size_t Port)
    {
        return true;
    }
}

int main()
{
    nmspace::MyClass::Class_Transmit = nmspace::MyFunc;
    return 0;
}

创建DLL后函数指针赋值导致错误

Function pointer assignment cause error after creating DLL

c++

function-pointers

class