How get the memory used by one process ( like the one shown in task manager )

object: How get the memory used by one process ( like the one shown in task
manager )

I want to build a routine which allowe me to detect the total used memory by
a process.
I tried using some code like the follow but the result I got is different
from the one showed in task manager:

       LPCVOID lpAddress;
       MEMORY_BASIC_INFORMATION mbi;
       HANDLE hProcess = GetCurrentProcess();
       ZeroMemory(&mbi,sizeof(mbi));
       mbi.BaseAddress=0;
       mbi.AllocationBase=0;
       mbi.RegionSize=0;
       mbi.AllocationProtect=PAGE_READWRITE;
       mbi.State= MEM_FREE | MEM_COMMIT | MEM_RESERVE;
       VirtualQueryEx(hProcess, lpAddress, &mbi, sizeof(mbi));
       StatusBar1->Panels->Items[1]->Text = String(mbi.RegionSize);

I suppose this code is wrong but I didn't know how is wrong.
Can someone help me ?

Regards, Ezno