我正在编写一个C ++程序,该程序在运行时动态加载dll并在该dll中调用一个函数。没问题,但是现在我想从dll中调用在C ++程序中定义的函数。
我的main.cpp看起来像这样:
#include <Windows.h>
#include <iostream>
typedef void(*callC)(int);
int main()
{
HINSTANCE dllHandle = LoadLibrary("D:\Libraries\lib.dll");
callC func = (callC)GetProcAddress(dllHandle, "callC");
func(42);
FreeLibrary(dllHandle);
}
// I want to call this function from my dll
void callableFromDll(){
}
被访问的dll的一部分在C中写成,如下所示:
#include <stdio.h>
void callC(int);
void callC(int i){
print(i);
// Call the C++ function
//callableFromDll();
}
我已经读过__declspec(dllimport)
和__declspec(dllexport)
属性,但是对于C ++来说真的很新,不知道这些是否是正确的用法,如果是,如何使用它们。
在您的C ++程序中:
extern "C" _declspec(dllexport) void callableFromDll(int value) {
printf("This function was called from the main process. Value: %d\n", value);
}
在您的DLL中:
typedef void(*callableFromDll)(int);
callableFromDll func;
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
func = (callableFromDll)GetProcAddress(GetModuleHandle(NULL), "callableFromDll");
func(69);
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}
GetModuleHandle(NULL)
返回父级的可执行句柄。
当LoadLibrary加载DLL时从exe控制台输出:
DLL_PROCESS_ATTACH
This function was called from the main process. Value: 69
cppfunction.exe (process 16336) exited with code 0.
Press any key to close this window . . .
extern "C"
告诉编译器不要将函数的名称编码为唯一的名称。编译器对名称进行编码,以便链接器可以分隔通用函数或变量名称。
请参见extern "C" and extern "C++" function declarations,Exporting from a DLL Using __declspec(dllexport) 和Importing function calls using __declspec(dllimport)。