DAQmx: How to query the list of devices in ANSI C?

[JKSH]

Hello,

LabVIEW has a DAQmx System property node, which has a Device Names item. This returns a list of DAQmx devices on my system.

I was looking for an equivalent function in the ANSI C library (http://zone.ni.com/reference/en-XX/help/370471AF-01/TOC3.htm ), but couldn't find anything. Does this function exist?

Thanks!

[bstreiff · Accepted solution]

You'll want to look in the "NI-DAQmx C Properties" section. The C equivalent to LabVIEW's DAQmx System→Device Names property is DAQmxGetSysDevNames.

[Kittenwhiskers]

Hello,

the DAQmxGetSysDevNames function uses a character pointer (char *data) as an argument. What should I use for this? Should I just define an empty character array and then use its pointer in the DAQmxGetSysDevNames function? I haven't been able to find an example ANSI C code for this function. As you can probably tell I am very new to programming. 

Regards, 

[bstreiff]

The documentation for that function, unfortunately, is quite lacking.

The operative documentation is How Do I Dynamically Choose the Size of an Array to be Passed to a NI-DAQmx C Function?, and my answer on Why does DAQmxGetDevAOVoltageRngs return 4 values? demonstrates the approach. That example was for a function returning an array of floating point values, but the same general principle applies with a string (in C, an array of characters)-- calling with a NULL pointer and a length of 0 will return the required buffer size, when you then have to allocate.

/* NOTE: for sake of brevity, error handling has been elided in this example */
int32 status;
int32 stringLength;

/* get number of characters */
stringLength = DAQmxGetSysDevNames(NULL, 0);

if (stringLength < 0) {
	/* handle error */
} else {
	char *deviceNames = (char *)calloc(stringLength, sizeof(char));
	if (!deviceNames) { /* handle allocation failure */ }

	status = DAQmxGetSysDevNames(deviceNames, stringLength);
	if (status < 0) { /* handle failure */ }

	printf("Devices: %s\n", deviceNames);

	free(deviceNames);
}

For properties that return a list of devices or channels, as DAQmxGetSysDevNames does, the format is (loosely) documented in Physical Channel Syntax; it is a comma-and-space separated list. For example:

cDAQ3, cDAQ3Mod1, cDAQ3Mod4, cDAQ3Mod6