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Programming

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Expression parser

Expression parser

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Posted by

Georgios (1 post)

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Date

Reply #60 on Wed 03 Nov 2010 08:03 PM (UTC)

Message

Hello Nick

As I can read from your comments and forum messages your expression parser is what I am looking for. The only problem is that I have to use it in a micro controller (ATMEL AVR) in C language.
A post from Jorick at 7th August 2007 has a similar situation (to change from c++ to c).
Have you the code in c ? Or any suggestion to port your code in c ?

Best regards
Georgios

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Posted by

Nick Gammon Australia (23,042 posts)

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Date

Reply #61 on Wed 03 Nov 2010 08:39 PM (UTC)

Message

The whole design is based on the way C++ works (like, getting variables by reference). To do it for C would be a rewrite.

Would the controller support Lua? That compiles in C. However I believe some micro chips have a different architecture that doesn't work with Lua.

- Nick Gammon

www.gammon.com.au, www.mushclient.com

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Posted by

Thierry (5 posts)

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Date

Reply #62 on Fri 07 Sep 2012 08:53 PM (UTC)

Message

Hello

Suppose a user enters an expression like this: (TT_123 * 10)/PT_870

How can I list the two parameters (TT_123 and PT_870) before evaluation to add the assignment
p[TT_123] = 100.0; (for example)
p[PT_870] = 0.56; (for example)

Thanks for your help

Thierry

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Posted by Nick Gammon Australia (23,042 posts) bio Forum Administrator

Date

Reply #63 on Fri 07 Sep 2012 11:50 PM (UTC)

Amended on Sat 08 Sep 2012 07:51 AM (UTC) by Nick Gammon

Message

It's not designed to do that right now. I gather you want to have it "query" for a variable value at runtime, is that right?

Non-defined variables currently default to zero. In particular around line 509:


      // not a function? must be a symbol in the symbol table
      double & v = symbols_ [word]; // get REFERENCE to symbol table entry

This creates the symbol if it doesn't exist, and it will default to zero. You would need to alter that line to do a lookup to see if the symbol exists, and if not have some way of obtaining it (eg. a callback function).

What might work could be to parse twice. First time you get zeroes for each symbol. Then look at the symbol table list to see what symbols get added. Change their values, and re-parse.

- Nick Gammon

www.gammon.com.au, www.mushclient.com

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Posted by

Thierry (5 posts)

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Date

Reply #64 on Sat 08 Sep 2012 07:03 AM (UTC)

Message

Hello

Yes, I need to get the information at run time. I scan the symbols map, update the values and call Evaluate a second time .... Working fine !!!

Thanks for that great class ... It will be used in the next release of a freeware called Genesis (www.tgmdev.be), an OPC data acquisition utility for people involved in process automation.

Thierry

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