Can't read registry key value

[Null]

Hello,
I'm trying to read a registry key value into struct but only 4 bytes are read:

#include <windows.h>
#include <winreg.h>
#include <iostream>
using namespace std;


struct mdd  // mounted device data
{
unsigned __int32 disk_signature; // mbr disk signature
unsigned __int64 offset;         // where partition begins (bytes)

};

// Get data from registry
int get_mdd(char *subkey,mdd *ret)
{
HKEY hkey;
DWORD type=REG_BINARY;
DWORD size=sizeof(mdd); // 12 bytes

memset(ret,0,sizeof(mdd));

RegOpenKeyEx(HKEY_LOCAL_MACHINE,"SYSTEM\\MountedDevices",0,KEY_READ,&hkey);
if(hkey==INVALID_HANDLE_VALUE) return -1;
RegQueryValueEx(hkey,subkey,0,&type,(BYTE*)ret,&size);

RegCloseKey(hkey);
return size;
}



int main()
{
mdd data;
get_mdd("\\DosDevices\\C:",&data);

cout <<"Disk signature:             "<<hex<<data.disk_signature<<dec<<endl; // works
cout <<"Partition begins in sector  "<<data.offset/512<<endl;               // doesn't work -- always zero

}

I don't know why but data.offset is always zero.
Maybe I pass mdd to RegQueryValueEx function incorrectly?

Thanks for help.

[kbw]

DWORD size=sizeof(mdd); // 12 bytes
As you've probably already noticed, it's the size of a pointer.

[Null]

DWORD size=sizeof(mdd); is correct.
The problem with my code was that data in registry is packed while struct mdd was not.

#include <windows.h>
#include <winreg.h>
#include <iostream>
using namespace std;

#pragma pack(1) 
struct mdd  // mounted device data
{
unsigned __int32 disk_signature; // mbr disk signature
unsigned __int64 offset;         // where partition begins (bytes)

};
#pragma pack(0)
// Get data from registry
int get_mdd(char *subkey,mdd *ret)
{
HKEY hkey;
DWORD type=REG_BINARY;
DWORD size=sizeof(mdd); // 12 bytes

memset(ret,0,sizeof(mdd));

RegOpenKeyEx(HKEY_LOCAL_MACHINE,"SYSTEM\\MountedDevices",0,KEY_READ,&hkey);
if(hkey==INVALID_HANDLE_VALUE) return -1;
RegQueryValueEx(hkey,subkey,0,&type,(BYTE*)ret,&size);

RegCloseKey(hkey);
return size;
}



int main()
{
mdd data;
get_mdd("\\DosDevices\\C:",&data);

cout <<"Disk signature:             "<<hex<<data.disk_signature<<dec<<endl;
cout <<"Partition begins in sector  "<<data.offset/512<<endl;  

}

[kbw]

Quite right.