Re: Cast pb

From:

"mlimber" <mlimber@gmail.com>

Newsgroups:

comp.lang.c++

Date:

25 Jul 2006 11:27:59 -0700

Message-ID:

<1153852079.814033.236280@i42g2000cwa.googlegroups.com>

Vincent RICHOMME wrote:

Hi,

I am trying to convert a C project into C++. This project is used to
hook some system calls on a Windows CE platform.

Here is the class definition:

class CHookBase
{
public:

CHookBase(DWORD dwSysCallAddr);
~CHookBase(void);

This should probably be virtual. See also
http://www.parashift.com/c++-faq-lite/newbie.html#faq-29.4.

     virtual void SetHook() = 0;
    virtual void InitHook();

private:
    const DWORD FIRST_METHOD;
    const DWORD CURRENT_METHOD;
    const int APICALL_SCALE;
    const int HANDLE_SHIFT;
    const DWORD METHOD_MASK;
    const DWORD HANDLE_MASK;

    BOOL m_bMode;
         DWORD m_dwPerm;
    CINFO** m_SystemAPISets;

    DWORD m_Tmp;
    DWORD m_ApiSet;
         DWORD m_Method;
    PFNVOID m_pfnOrgFunc;
};

#include "hookbase.h"
class CCreateFileHook : public CHookBase
{
public:

//----------------------- SIGNATURE OF FUNCTIONS TO
HOOK--------------------//
    typedef HANDLE t_CreateFile
        (
        LPCTSTR lpFileName,
        DWORD dwDesiredAccess,
        DWORD dwShareMode,
        LPSECURITY_ATTRIBUTES lpSecurityAttributes,
        DWORD dwCreationDisposition,
        DWORD dwFlagsAndAttributes,
        HANDLE hTemplateFile
        );

    CCreateFileHook(DWORD dwSysCallAddr);
    ~CCreateFileHook(void);

static HANDLE _CreateFileHook( LPCTSTR lpFileName, DWORD

All identifiers beginning with an underscore and a capital letter are
reserved for the implementation. Better change this.

dwDesiredAccess, DWORD dwShareMode,
LPSECURITY_ATTRIBUTES lpSecurityAttributes, DWORD dwCreationDisposition,
DWORD dwFlagsAndAttributes, HANDLE hTemplateFile);

virtual void SetHook();

};

and here is the implementation:

/*static*/
HANDLE CCreateFileHook::_CreateFileHook( LPCTSTR lpFileName, DWORD
dwDesiredAccess, DWORD dwShareMode, LPSECURITY_ATTRIBUTES
lpSecurityAttributes, DWORD dwCreationDisposition, DWORD
dwFlagsAndAttributes, HANDLE hTemplateFile)
{
HANDLE H = ((t_CreateFile*) m_pfnOrgFunc

Where is m_pfnOrgFunc defined? What is its type?

)(lpFileName,dwDesiredAccess,dwShareMode,lpSecurityAttributes,dwCreationDisposition,dwFlagsAndAttributes,hTemplateFile);
    DWORD Err = GetLastError();

        SetLastError(Err);
    return H;
}

However when I compile I got the following message :
CCreateFileHook.cpp(21) : error C2440: 'type cast' : cannot convert from
'' to 't_CreateFile (__cdecl *)'
         The expression being converted is not valid

You'll note the empty quotes. Apparently the compiler doesn't know what
type it's converting from.

In C this cast is allowed .........

Maybe, but prefer C++-style casts since they're clearer and less
dangerous. Better still, avoid casting at all.

For info :

HANDLE is a void*
PFNVOID is defined as a pointer to function returning void and taking 0
parameter (=typedef void(PFNVOID*)(void)

How can I fix that ?

First of all, read the guidelines about posting problematic code:

http://parashift.com/c++-faq-lite/how-to-post.html#faq-5.8

Reduce this down to a simpler problem, and you'll either find your
answer or you can post it for a better response.

Cheers! --M