Error restore virtual machine snapshot in Virtual Box

Question

I use VirtualBox and Virtual Box API Microsoft Com C++ for my project. It’s VirtualBox 6.0.6 Software Developer Kit (SDK) and VirtualBox 6.0.6 platform packages.
I have a problem. I want to recover a snapshot system, that was created early, but the program shows errors.
My code with comments:

HRESULT rc; 

IVirtualBoxClient *virtualBoxClient = nullptr; 
IVirtualBox *virtualBox = nullptr; 
IMachine *machine = nullptr; 
ISession *session = nullptr; 
IProgress *progress = nullptr; 
ISnapshot* snapshot = nullptr; 

BSTR sessiontype = SysAllocString(L"gui"); 
BSTR machineName = SysAllocString(L"Win7x64"); 


HRESULT rc = CoCreateInstance(CLSID_VirtualBoxClient, NULL, CLSCTX_INPROC_SERVER, IID_IVirtualBoxClient, (void**)&virtualBoxClient); 

rc = virtualBoxClient->get_VirtualBox(&virtualBox); 

// looking for a machine with a name Win7x64 
rc = virtualBox->FindMachine(machineName, &machine); 

// create a session object 
rc = CoCreateInstance(CLSID_Session, NULL, CLSCTX_INPROC_SERVER, IID_ISession, (void**)&session); 
if (!SUCCEEDED(rc)) 
{ 
printf("Error creating Session instance! rc = 0x%x\n", rc); 
break; 
} 

// block the machine 
machine->LockMachine(session, LockType::LockType_Shared); 

// the name of the snapshot system 
BSTR snapshotUUID = SysAllocString(L"Win7_test_snapshot"); 
// looking for a snapshot system 
rc = machine->FindSnapshot(snapshotUUID, &snapshot); 
// recover snapshot. ERROR: variable rc - E_NOTIMPL Not implemented. 
rc = machine->RestoreSnapshot(snapshot, &progress); 

printf("Starting VM, please wait ...\n"); 
//waiting for the end of the operation. Abnormal termination- progress == nullptr ! 
rc = progress->WaitForCompletion(-1); 
// unlocking the machine 
rc = session->UnlockMachine(); 
if (!SUCCEEDED(rc)) 
{ 
printf("Error restore state machine!\n"); 
break; 
}

Also, I created a simple C # application, and got the exact same error there. What's the matter? This is mistake API ? I even changed the OS (virtual) many times:

  static void Main(string[] args)
    {
        VirtualBox.VirtualBox virtualBox = new VirtualBox.VirtualBox();
        IMachine vmMachine = virtualBox.FindMachine("Win7x64VB");
        Session session = new Session();
        vmMachine.LockMachine(session, LockType.LockType_Shared);
        IConsole console = session.Console;

        // Restore snapshot
        ISnapshot snapShot = vmMachine.FindSnapshot("Win7_snapshot1");

        IProgress snapShotProgress = vmMachine.RestoreSnapshot(snapShot);
        snapShotProgress.WaitForCompletion(300000);

        // unlock before launch VMProcess
        session.UnlockMachine();

        IProgress launchVmProgess = vmMachine.LaunchVMProcess(session, "gui", "None");

        launchVmProgess.WaitForCompletion(300000);
    }

Can you help me, how to fix call method error “ RestoreSnapshot - E_NOTIMPL Not implemented” or how to restore a snapshot of the system correctly? Thank you.

P.S.: I asked this question on the official forum, but no one helps me.

Answer 1

I found a solution of the problem. Snapshot should be restored with the system that is current for the session. So code will be as follows:

HRESULT rc = machine->LockMachine(session, LockType::LockType_Shared);
rc = machine->FindSnapshot(snapshotUUID, &snapshot);
IMachine* currentMachine(nullptr);
rc = session->get_Machine(&currentMachine);
rc = currentMachine->RestoreSnapshot(snapshot, &progress);
rc = progress->WaitForCompletion(300000);
rc = session->UnlockMachine();

It works with this code.