Convert ViChar to double.

[FredTest]

I am trying to convert a ViChar to a double and have tried using the following exmaple...

static ViChar daqmeasure[256];

double measurement;

measurement = (double) daqmeasure;

I am getting the following error...

Cast from pointer to ViChar to double is illegal.

Can someone explain a possible solution?\

ThanksNAdvance

[mvr]

Assuming the ViChar daqmeasure[256] variable contains a floating point double value in binary form (and is not an ascii string) you can convert it by

measurement = *(double*)daqmeasure;
daqmeasure is a pointer, so CVI would not let you cast it to a double directly.

If you want to step through the array use
measurement[i] = *(double*)&daqmeasure[i*sizeof(double)]; in a loop.

If the data in ViChar is really a string value (easy to see by looking at the array in the debugger) you can use atof() to convert the string to a double value or if it is an array of doubles stored in a string use the CVI function Scan().
 

[FredTest]

It is a string but your instructions were not clear...

Thanks!

[jr_2005]

Maybe:

    measurement = atof (daqmeasure);

will meet your needs?

JR

[FredTest]

JR_2005

I'm new to LabWindows and had never seen or heard of the atof command.

I apologize for my stupor.

Thanks alot!

FredTest

[Matt M.]

Hi Fred,

The ViChar data type is just like a regular char datatype; however, VISA has placed a wrapper around it to increase portability. So, simple ViChar casting would work in the following situation:

ViChar mychar;
double mydouble;
mydouble = (double) mychar;

However, your case is different beacuse ViChar is an array. In your case you can use one of two methods to convert the data to a double.

1) If the data is a string in the character array, for instance:

daqmeasure[0] = '7';
daqmeasure[1] = '.';
daqmeasure[2] = '3';
daqmeasure[3] = '2';

Then you should use the atof function:

measurement = atof (daqmeasure);

2) If the data is in a binary string you can follow Function to Convert Binary in String Format to a Float or Double.
With some minor tweaks, this could help you convert a binary string to a double.

Matt Mueller
NI