evaluating logical boolean expressions

hi,

I am looking for a library to aid me in evaluating Boolean expressions.
For example, i have an expression like this:

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(1*(5+3)+9*65/5-(354*4565*5643+98) >= 12345) && ( 654*987+123 || (2345 > 23423 && 1 != 2)))

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(it can alos be much longer!)

and would like to evaluate them to a true/false boolean.
My dear gcc would kick some *** here with its static evaluation, but it`s way too complicated to use a compiler or the like for this.

There are tons of libraries to calculate the (numerical) result of a mathematical expression, but this is not what i want to do.

Perhaps you should start by defining the grammar of these boolean expressions. After that, it becomes a question of whether you want to write your own parser or use some tool to create a parser for you.

forgot that, sorry. :)

Standard math/c++ set of expressions, i would say, ie:

<,>,>=,<=,&&,||, nested brevets,*,+,-,/, etc.

If i was to write my own parser, would you know of any "reference" project i could learn from or base on?

Quote:

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Originally Posted by tuli

forgot that, sorry. :)

Standard math/c++ set of expressions, i would say, ie:

<,>,>=,<=,&&,||, nested brevets,*,+,-,/, etc.

If i was to write my own parser, would you know of any "reference" project i could learn from or base on?

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Look up "grammar" and "recursive descent parsers". You need to formally define the grammar first, then from the grammar (production) rules, you create the parser.

Regards,

Paul McKenzie

Quote:

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Originally Posted by tuli

I am looking for a library to aid me in evaluating Boolean expressions.

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you can use the boost.Spirit library to write a BNRF based parser relatively quickly ( the "Qi" library component, more specifically; there are also a lexer and an output generator library components but you'll probably not need them ... ). Used in conjunction with boost.Phoenix you can process the expression in-place while parsing, including grammar error handling.

Quote:

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Originally Posted by tuli

(it can alos be much longer!)

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so, are those expressions human or computed generated ? in the latter case you don't need a parser, just store the expression in a computer-understandable representation directly.

An alternative approach would be to load a linkable script language. Writing your own expression parser of "mini language" to do this will take a considerable amount of development time.

One example is LUA (www.lua.org) which is pretty easy to integrate into a C/C++ program. But there are many others.

Another way out would be to take the expression and form it into a VBScript or javascript and use the wscript.exe to evaluate it for you.