"using VirtualFn1_t = void(__thiscall)(void thisptr);" 在 C++ 中是什么意思？

Question

我在阅读源代码时试图理解挂钩对于虚函数方法 table 从维基百科挂钩我遇到了这条线。

using VirtualFn1_t = void(__thiscall*)(void* thisptr);

我不知道它是什么意思。是否将 void 指针转换为调用约定并将其重新转换为 void 指针并将其用作 VirtualFn1_t 别名。我也想了解 void (__thiscall*)(void* thisptr) 和 (__thiscall*)(void* thisptr) 是什么意思。

这是来自维基百科的完整资源。

#include <iostream>
#include "windows.h"

using namespace std;

class VirtualClass
{
public:

    int number;

    virtual void VirtualFn1() //This is the virtual function that will be hooked.
    {
        cout << "VirtualFn1 called " << number++ << "\n\n";
    }
};




using VirtualFn1_t = void(__thiscall*)(void* thisptr); 
VirtualFn1_t orig_VirtualFn1;


void __fastcall hkVirtualFn1(void* thisptr, int edx) //This is our hook function which we will cause the program to call instead of the original VirtualFn1 function after hooking is done.
{
    cout << "Hook function called" << "\n";

    orig_VirtualFn1(thisptr); //Call the original function.
}




int main()
{
    VirtualClass* myClass = new VirtualClass(); //Create a pointer to a dynamically allocated instance of VirtualClass.

    void** vTablePtr = *reinterpret_cast<void***>(myClass); //Find the address that points to the base of VirtualClass' VMT (which then points to VirtualFn1) and store it in vTablePtr.

    DWORD oldProtection;
    VirtualProtect(vTablePtr, 4, PAGE_EXECUTE_READWRITE, &oldProtection); //Removes page protection at the start of the VMT so we can overwrite its first pointer.

    orig_VirtualFn1 = reinterpret_cast<VirtualFn1_t>(*vTablePtr); //Stores the pointer to VirtualFn1 from the VMT in a global variable so that it can be accessed again later after its entry in the VMT has been 
                                                                  //overwritten with our hook function.

    *vTablePtr = &hkVirtualFn1; //Overwrite the pointer to VirtualFn1 within the virtual table to a pointer to our hook function (hkVirtualFn1).

    VirtualProtect(vTablePtr, 4, oldProtection, 0); //Restore old page protection.

    myClass->VirtualFn1(); //Call the virtual function from our class instance. Because it is now hooked, this will actually call our hook function (hkVirtualFn1).
    myClass->VirtualFn1();
    myClass->VirtualFn1();

    delete myClass;

    return 0;
}

Answer 1

VirtualFn1_t 被定义为以下类型的别名：指向采用 void* 参数、返回 void 并使用 __thiscall 调用约定的函数的指针。

Answer 2

自 C++11 起，using 是创建类型别名的新方法。它与 typedef.

相似（但更灵活）

本题中的using语句：

using VirtualFn1_t = void(__thiscall*)(void* thisptr);

等同于 typedef:

typedef void (__thiscall *VirtualFn1_t)(void* thisptr);

这两个语句都将 VirtualFn1_t 定义为一种新类型，它是一个指针指向一个函数：

接受一个void*作为输入参数
使用 __thiscall 调用约定
returns一个void.

orig_VirtualFn1 被声明为 VirtualFn1_t 类型的变量（因此 orig_VirtualFn1 是一个指针），并指向原始 VirtualClass::VirtualFn1() 的内存地址方法在运行时，在 VirtualClass class 的 vtable（虚方法 table）被修改之前，使 VirtualFn1() 的插槽指向 hkVirtualFn1() 钩子函数代替。

"using VirtualFn1_t = void(__thiscall)(void thisptr);" 在 C++ 中是什么意思？

What does "using VirtualFn1_t = void(__thiscall)(void thisptr);" means in c++?

windows

hook

winapi

"using VirtualFn1_t = void(__thiscall*)(void* thisptr);" 在 C++ 中是什么意思？

What does "using VirtualFn1_t = void(__thiscall*)(void* thisptr);" means in c++?

windows

hook

winapi

"using VirtualFn1_t = void(__thiscall)(void thisptr);" 在 C++ 中是什么意思？

What does "using VirtualFn1_t = void(__thiscall)(void thisptr);" means in c++?