virtual comport auto detect

[patil1983]

HI 

I am trying to comport auto detect,

i am uisng  status = viFindRsrc (defaultRM, "ASRL[0-9]*::?*INSTR", &find_list, &retCnt, instrDesc);  funtion  to detect  port , but its working  upto port  9  after 9 it not detecting  correct one . please give an idea how  tp slove this  issue.   ( comport  may be  1 to  255). 

  thanks

[nyc_(is_out_of_here)]

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@patil1983 wrote:

HI 

I am trying to comport auto detect,

i am uisng  status = viFindRsrc (defaultRM, "ASRL[0-9]*::?*INSTR", &find_list, &retCnt, instrDesc);  funtion  to detect  port , but its working  upto port  9  after 9 it not detecting  correct one . please give an idea how  tp slove this  issue.   ( comport  may be  1 to  255). 

  thanks

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That's because you are telling it to look for com ports 0-9.

[Wolfgang]

nyc, doesn't the * after the [0-9] mean zero or more occurrences of the preceding character or expression?

'or more' should include ports 10, 100, ..., no?

[nyc_(is_out_of_here)]

I am no regular expression expert.

the [0-9] means one digit 0 ... 9

the * means 0 or more times

[Wolfgang]

so this means that 'That's because you are telling it to look for com ports 0-9.' is not correct... it should also find ports with numbers larger than 9...

[nyc_(is_out_of_here)]

I am not sure where the OP got his example code from.

The LabVIEW example VI at https://forums.ni.com/t5/Example-Code/Obtaining-a-List-of-Only-the-COM-Ports-as-VISA-Resource-Names/...   uses the expression ASRL?*::INSTR  which is very similar to what I used to find my USB scope.

It doesn't look like it is a real regular expression.

According to the LabVIEW Help,

  ?   matches any one character

  *  matches any 0 or more occurences of the preceding character or expression.

 [list]   matches any one character from the enclosed list. You can use a hyphen to match a range of characters

[nyc_(is_out_of_here)]

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@Wolfgang wrote:

so this means that 'That's because you are telling it to look for com ports 0-9.' is not correct... it should also find ports with numbers larger than 9...

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No, if it was a regular expression it will NOT find numbers greather than 9. 

I suggest that you look up what [0-9] actually means for a true regular expression.

Brackets means a list and with the hyphen, you are looking 0 or 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9.

That is it.

[Wolfgang]

if you say so...

all I can tell is that viFindRsrc ( resource_manager_handle, "ASRL[0-9]*::?*INSTR", &find_handle, &return_count, instrument_descriptor ); does find all my serial ports, and I do have more than 30

[RobertoBozzolo]

Findind the correct search expression can be a challenge!

If I search with "ASRL[0-20]*::?*INSTR" function fails to recognize port 4, while "ASRL[0-24]*::?*INSTR" finds it; "ASRL[0-256]*::?*INSTR" fails too 

However, the expression in brackets is not a simple list, since even "ASRL[0-4]*::?*INSTR" finds port 10 (for what is worth, "ASRL[1-4]*::?*INSTR" doesn't locate port 10).

I am not an expert on Visa and even less on regular expressions, but it seems to me that "ASRL?*INSTR" as mentioned before should be the best search string. Next he will need to discriminate the parallel port if it exists in the system, which is counted too by the call.

[Wolfgang]

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@RobertoBozzolo wrote:

Findind the correct search expression can be a challenge!

If I search with "ASRL[0-20]*::?*INSTR" function fails to recognize port 4, while "ASRL[0-24]*::?*INSTR" finds it; "ASRL[0-256]*::?*INSTR" fails too 

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Roberto, I would assume that [0-2]* means 0,1,2,00,01,02, ... and accordingly it will not find port 4. The same is true for [0-256]*.

And, for the same reason, ASRL[0-4]* finds port 10 because 0-4 includes 0 and 1, and * means repetitive.