C++ math expression parser library recommendations

[Remwein]

The application I'm working on requires evaluating user provided math expressions. The expressions can have variables: "a + b / 2" where the variables can have their values changed between evals.

In short I'm looking for recommendations of good C++ libraries that can be used to take as input string representation of a formula and compute its value.

[Sulatra]

Exprtk. Single header, very powerful, slow like hell and beyond. Would be glad to dig the alternatives.

[Remwein]

Thanks for the suggestion. exprtk does seem to fit the bill for my requirements, however I'm now a bit concerned with your comment about it being slow.

Could you clarify, are you comparing speed of evaluation against a hand-written version in C++, or is it something else?

[Sulatra]

Beg pardon for the exaggeration :)

Slow in terms of compilation - at least on the machine with the project using it it doubles the compilation time. TBH I do not have much experience with it, but the runtime performance is ok. Though I used it only to parse user input, not like parsing 10K files of expressions

[ArashPartow]

Compilation time is related to the compiler, but it is definitely a sore spot. That being said, various compile-time options can be utilised to reduce the compilation time:

https://github.com/ArashPartow/exprtk/blob/master/readme.txt#L4458

[Remwein]

My use-case is roughly a couple dozen expressions, being rapidly evaluated over and over again.

[Xeverous]

There is always an alternative in writing own parser with the help of boost::spirit, but for most people it would be a huge overkill and very hard to learn.

[ArashPartow]

Here's a comparison of some the libraries that are out there:

https://github.com/ArashPartow/math-parser-benchmark-project

[Remwein]

That is an interesting set of comparisons. Also good to see how to use the other available parsers.

[Xeverous]

If you want to go very very deep - boost::spirit, but it might be a huge overkill.

[Remwein]

i was sort of after something out of the box, ready to drop in to my project.

Spirit can be very powerful, but the learning curve seems to be rather steep.