Typecasting from struct to LPVOID

Question

Worked fine before I threw it into a class. Any help for resolving this typecasting error?

Error

error C2440: 'type cast' : cannot convert from 'IAT CInjector::* ' to 'LPVOID'

Code Referenced

WriteProcessMemory(CInjector::_hProc, 
    CInjector::_iatBaseAddress, 
    (LPVOID) & CInjector::_iat, // typecasting error?
    sizeof (IAT), 
    NULL);

Class

class CInjector
{
private:
    ...
    IAT _iat;
    ...
}

Typedef

typedef struct _IAT {
    PLOADLIBRARYA pLoadLibraryA;
    PGETPROCADDRESS pGetProcAddress;
    FNMESSAGEBOX fnMessageBox;
} IAT;

Answer 1

The problem is that &CInjector::_iat is a pointer-to-class-member, not a real pointer. Since _iat isn't static, each class has its own copy of it, and so &CInjector::_iat is not an address, but rather is typically an offset into a class. You can use it with the "pointer-to-member-selection" operator .* :

CInjector myCInjector;
IAT CInjector::* ptr = &CInjector::_iat;
myCInjector.*ptr = /* ... */

The C++ standard prohibits conversions between pointers-to-class-members and raw pointers because often they look different in memory - pointers-to-class-members often store some offset value so that they work correctly in multiple inheritance or in the presence of virtual functions, for example.

To fix this, you probably want to do one of two things. First, you can mark CInjector::_iat static , which means that there's only one copy of it. Consequently, &CInjector::_iat now refers to a concrete object, which is indeed a regular pointer, and the above code will work. Second, you can get a concrete instance of CInjector and then take the address of its _iat field. Since this refers to a specific object's field, you'll get back a raw pointer.

Hope this helps!

Answer 2

You cannot convert pointer to member into a pointer to an object. Read more here .