Kexpr is a lightweight two-file library for parsing and evaluating math expressions. It supports common math functions and works with variables. This library was developed in 2015 as part of the klib library and is now separated into this repo. Some of the design choices at the time may be questionable and error checking is not thorough, but the library is largely usable.

To use kexpr as a library, you may copy both kexpr.h and kexpr.c to your own source code tree and call functions in the header file. Kexpr also comes with a simple command-line interface. To compile:

gcc -O3 -Wall -std=c99 -DKE_MAIN kexpr.c -o kexpr

Here are some examples:

./kexpr "2+5*2"                  # output 12 (simple arithmetic)
./kexpr "2+5*exp(-1)"            # output 3.8394 (builtin functions)
./kexpr "2+5*exp(x+y)" x=-2 y=1  # output 3.8394 (variables)
./kexpr "2^1"                    # output 3 (bit operation)

The following examples cause parse errors:

./kexpr "5*"
./kexpr "5*exp("
./kexpr "5*exp)"
./kexpr "5*exp()"
./kexpr "5*exp(4,5)"

An example C program to use the library:

// compile with: gcc -O2 this-prog.c kexpr.c
#include <stdio.h>
#include "kexpr.h"
int main(void) {
  int err; // error code returned to this variable
  kexpr_t *e = ke_parse("2+3*x", &err); // parse expression
  ke_set_real(e, "x", 5); // set the value of variable "x"
  printf("%f\n", ke_eval_real(e, &err)); // output 17
  return 0;
}