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.
I am looking for a library to aid me in evaluating Boolean expressions.
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.
Originally Posted by tuli
(it can alos be much longer!)
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.