Scan from string does not find number

[pbuerki]

Hello,

I ran into the following problem: I have a string returned from an instrument through the serial interface. I would like to extract the numerical value from the string (double precision format). If I use the scan from string function, it does not find the numerical value. Similarly, if I use the Match Pattern function and go looking for the character "[", it does not find it returning offset past match of -1. What is going on?

Note that I cannot expect that the instrument always returns 9 characters before the start of the number.

Thanks for your help.

Peter 

(using LabVIEW 8.5 on a WinXP machine)

[Matt_W1]

Scan from string assumes what you scanning for starts at the initial scan location. And since your string doesn't start with a number (or white space followed by a number) it doesn't find anything. The '[' character has special meaning for the match function so you have to escape it (use '\['). If you escape the '[' character and feed the offset past match into the initial scan location, then the scan from string will read the number.

[jcarmody]

A Regular Expression will find your number.

-? will look for an optional minus sign

\d* looks for zero or more digits

\.? looks for an optional decimal point (the \ escapes the special 'dot' character)

\d+ gets any digits past the decimal point

[jcarmody]

I'd sure appreciate if someone would tell me why \d* doesn't work where \d+ does.

[Stephen_C]

Interesting that one Jim,

I think it must be that everything in your regex is optional if you use \d* in both places.

If we add something that is fixed, like changing the \.? to \. it will match the .

So I suspect that we just must have something concrete in the regex for it to work at all

With a numeric, that is no problem anyway as we would always have a digit somewhere.

In your example I guess it doesnt matter which \d is * and which is +

For the original poster, you could expand the regex to include all floting point numbers by searching for regex [+-]?\d+[.]?\d*+(?:[eE][+-]?\d+)?

Regards,

Steve

[JDinkins · Accepted solution]

Try this:

[jcarmody]

I tried to drag-n-drop it onto a BD.  Kudos, anyway.  🙂

[JDinkins]

Alright, here's the snippet

[pbuerki]

Thank you all for offering several different solutions to my issue. All of them work fine. Thanks again.

[ben64]

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@Stephen C wrote:

For the original poster, you could expand the regex to include all floting point numbers by searching for regex [+-]?\d+[.]?\d*+(?:[eE][+-]?\d+)?

Regards,

Steve

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This regex can be simplified to [Ee+-\d.]+

Ben64