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The NMX DLL allows having multiple connections to different devices, even though in most applications one connection to one device is used.

In order to distinguish between multiple connections, a unique handle is assigned for each of them by the NMX DLL.

 

Technically spoken, a handle is nothing else than a pointer to an address space managed by the NMX DLL. This is a common programming technique.

The pointer itself resides outside the NMX DLL in the user application. It is assigned if a connection has been established successfully (see NMX_DeviceIPv4Open_1). It is then used in almost every DLL function, to identify the relevant connection. It is deleted by closing the connection (see NMX_DeviceClose_1).

 

The Handle has the following type definition (C-Code):

typedef void* NMX_PHANDLE;

 

For each connection a handle must be declared. In case only one connection is used, the declaration looks as follows:

NMX_PHANDLE pHandle = NULL;

 

Note for the .Net DLL: Using the .Net DLL, the handle uses the type System::IntPtr. The basic concept is the same. In case only one connection is used, the declaration in C# looks as follows:

IntPtr pDevice = IntPtr.Zero;

 

Further information, if you use multiple connections / handles:

Inside the NMX DLL, each connection / handle has its own memory and its own communication tasks. Talking in object orientated programming, a separate object is created for each handle.

If notifications are used, these must be registered for each handle separately.