有没有一种方法可以在容器中存储不同的函数指针类型

Question

In the below code, I'm trying to store function pointers in a vector but each function pointer has a different signature.

The idea of the below code is that when I load a DLL, I simply use a loop to load all functions from the DLL into the vector. Then when I want to call a function, I just call it by name or index and pass a variable amount of arguments. But I really want to call the functions the same way that I loaded them: via a loop.

#if defined _WIN32 || defined _WIN64
#include <windows.h>
#else
#include <dlfcn.h>
#endif

#include <iostream>
#include <cstdint>
#include <vector>
#include <functional>

class Library
{
    private:
        void* Module;

    public:
        Library(std::string Library);
        ~Library();

        template<typename T>
        T AddressOf(std::string FunctionName);

        template<typename T>
        bool AddressOf(T &FunctionDefinition, std::string FunctionName);

        template<typename T, typename ...Args>
        auto CallFunction(void* Function, Args... args) -> decltype(reinterpret_cast<T>(Function)(args...));
};

Library::Library(std::string Library)
{
    #if defined _WIN32 || defined _WIN64
    this->Module = LoadLibrary(Library.c_str());
    #else
    this->Module = dlopen(Library.c_str(), RTLD_LAZY);
    #endif
}

Library::~Library()
{
    #if defined _WIN32 || defined _WIN64
    FreeLibrary(static_cast<HMODULE>(this->Module));
    #else
    dlclose(this->Module);
    #endif
}

template<typename T>
T Library::AddressOf(std::string FunctionName)
{
    #if defined _WIN32 || defined _WIN64
    return reinterpret_cast<T>(GetProcAddress(static_cast<HMODULE>(this->Module), FunctionName.c_str()));
    #else
    return reinterpret_cast<T>(dlsym(this->Module, FunctionName.c_str()));
    #endif
}

template<typename T>
bool Library::AddressOf(T &FunctionDefinition, std::string FunctionName)
{
    return (FunctionDefinition = this->AddressOf<T>(FunctionName));
}

template<typename T, typename ...Args>
auto Library::CallFunction(void* Function, Args... args) -> decltype(reinterpret_cast<T>(Function)(args...))
{
    return reinterpret_cast<T>(Function)(args...);
}





std::vector<void*> Functions;

typedef void (*Message)(const LPCSTR sometext);
typedef void (*MessageEx)(const LPCSTR sometext, const LPCSTR title);
typedef int (*Add)(int X, int Y);
typedef int (*Subtract)(int X, int Y);

int main()
{
    Library L("TestDll.dll");
    std::array<std::string, 4> List = {"Message", "MessageEx", "Add", "Sub"};

    /** Get Function Addresses.. **/
    for (std::size_t I = 0; I < List.size(); ++I)
    {
        Functions.push_back(L.AddressOf<void*>(List[I]));
    }

    /** Call Functions.. **/
    L.CallFunction<Message>(Functions[0], "Hello World!");
    L.CallFunction<MessageEx>(Functions[1], "Hello World!", "DLL MessageBox Title");

    std::cout<<L.CallFunction<Add>(Functions[2], 5, 7)<<"\n";
    std::cout<<L.CallFunction<Subtract>(Functions[3], 7, 5)<<"\n";

    return 0;
}

Is there a better way of re-writing my CallFunction class member or a way to retain function signature somehow or Map the name of the function to its signature? I don't mind writing out the typedefs but I hate having to put them as the template argument so that it can cast to it so if I could somehow have the vector store different function signatures would be best but any solutions are welcomed.

EDIT: To make things clear, I want to somehow figure out the function signature given its arguments. Ex:

//If I do:

CallFunction<int>(FuncPtr, "Subtract", 10, 5);

//It would do:


template<typename T, typename ...Args>
auto Library::CallFunction(void* Function, Args... args) -> decltype(reinterpret_cast<T>(Function)(args...))
{
    return  //using args, figure out the function signature, call it, and return int.
}

Answer 1

To me, this seems rather contrived. You need the right function in the right place with the right arguments, for the right name. If you declare a function pointer typedef , and use a single line reinterpret_cast to assign the function, you need a good 40+ functions before it's up to the code you have provided here - and that's simple step and repeat type code, so it's easy to follow and easy to maintain. No templates, no variable arguemnts, etc.

Obviously, you'd still have to produce a function that returns a void * from a name. But that would be just what you have now minus the reinterpret_cast .