Data Type TaskHandle in DAQmx

[Tommysaurus]

I'm trying to create a DLL wrapper to access a few of the DAQmxBase functions for a hardware project. I keep getting the error "Cannot convert from 'unsigned long *' to 'unsigned long **'", where I call the function DAQmxBaseCreateTask(taskName, taskHandle). A little research revealed that the header file 'NIDAQmxBase.h' defines the data type 'TaskHandle' as a pointer to unsigned long and 'NIDAQmx.h' does not.

NIDAQmxBase:

typedef unsigned long uInt32;

...

typedef uInt32 *TaskHandle;

NIDAQmx.h:

typedef unsigned long uInt32;

...

typedef uInt32 TaskHandle;

Both header files define the function call as:

int32 __CFUNC     DAQmxCreateTask          (const char taskName[], TaskHandle *taskHandle);

Doesn't that result in 'taskHandle' being a pointer to a pointer to unsigned long in 'NIDAQmxBase'? I can get the DLL compiled if I remove the '*' in the function prototype but then it crashed when I run the application. Has anyone hit this wall?

[WM_John_Weeks]

How interesting! That could ultimately cause some problems on 64-bit systems.

But for your problem, can't you simply use nidaq.h with your dll wrapper, and use the TaskHandle type? Why do you need to know the type of a TaskHandle? Are you trying to call the function with the basic types instead of using TaskHandle?

I would expect this code to compile with either header:

#include "nidaq.h"

...

TaskHandle h;
DAQmxCreateTask("", &h);

The underlying type of h will be different, but the call to DAQmxCreateTask will pass a pointer to whatever a TaskHandle is on either system.

Of course, all this ignores the fact that with DAQmx Base, the call is DAQmxBaseCreateTask().

[Tommysaurus]

Thanks, John. As an experiment I switched my code to use the NIDAQmx.h & .lib and it just worked! There's something funny about the Base version.

[WM_John_Weeks]

There are lots of funny things about DAQmx Base!