About OpenSCManager and OpenService函数的使用

如下所示：
a := OpenSCManager(PChar(ServerName),nil,SC_MANAGER_ALL_ACCESS);
if a <= 0 then Exit;
b := OpenService(a,PChar(SvrName),SERVICE_ALL_ACCESS);
if b <= 0 then Exit;
try
Result := StartService(b,0,c);
CloseServiceHandle(b);
CloseServiceHandle(a);
except
CloseServiceHandle(b);
CloseServiceHandle(a);
Exit;
end;
但这样使用总不成功，是不是这两个函数使用上有问题，请赐教！
end;