获取进程用户名c ++

我在做一个像app的taskmanager。对于windows，我可以得到所有的系统进程，现在我想获得进程的用户名。我得到的代码从网。

i am making a taskmanager like app. for windows,i can get all the system processes,now i want to get process's username.I got the code from net.

void enableDebugPrivileges()
{
    HANDLE hcurrent=GetCurrentProcess();
    HANDLE hToken;
    BOOL bret=OpenProcessToken(hcurrent,40,&hToken);
    LUID luid;
    bret=LookupPrivilegeValue(NULL,SE_LOAD_DRIVER_NAME, &luid);
    TOKEN_PRIVILEGES NewState,PreviousState;
    DWORD ReturnLength;
    NewState.PrivilegeCount =1;
    NewState.Privileges[0].Luid =luid;
    NewState.Privileges[0].Attributes=2;
    AdjustTokenPrivileges(hToken,FALSE,&NewState,28,&PreviousState,&ReturnLength);
}

char *GetProcessUsername(HANDLE *phProcess, BOOL bIncDomain) 
{
    static char sname[300];
    HANDLE tok = 0;
    HANDLE hProcess;
    TOKEN_USER *ptu;
    DWORD nlen, dlen;
    char name[300], dom[300], tubuf[300], *pret = 0;
    int iUse;

    //if phProcess is NULL we get process handle of this
    //process.
    hProcess = phProcess?*phProcess:GetCurrentProcess();

    //open the processes token
    if (!OpenProcessToken(hProcess,TOKEN_QUERY,&tok)) goto ert;

    //get the SID of the token
    ptu = (TOKEN_USER*)tubuf;
    if (!GetTokenInformation(tok,(TOKEN_INFORMATION_CLASS)1,ptu,300,&nlen)) goto ert;

    //get the account/domain name of the SID
    dlen = 300;
    nlen = 300;
    if (!LookupAccountSidA(0, ptu->User.Sid, name, &nlen, dom, &dlen, (PSID_NAME_USE)&iUse)) goto ert;


    //copy info to our static buffer
    if (dlen && bIncDomain) {
    strcpy(sname,dom);
    strcat(sname,"");
    strcat(sname,name);
    } else {
    strcpy(sname,name);
    }
    //set our return variable
    pret = sname;

    ert:
    if (tok) CloseHandle(tok);
    return pret;
}
int main(){
    enableDebugPrivileges();
    DWORD dwPID=3436;        
    HANDLE  hProcess_i = OpenProcess(PROCESS_QUERY_INFORMATION, FALSE, dwPID);
    printf("%s",GetProcessUsername(&hProcess_i,0));
}

它适用于系统和curr。用户进程，但不是为网络服务和本地服务，我得到null string.please告诉我如何获得这些进程的用户名。
感谢。

Its working well for system and curr. user processes but not for NETWORK SERVICE and LOCAL SERVICES and i got null string.please tell how can i get usernames of these processes too. thanks.