State machine module

This modules provides helper function to implement Finite State Machines (http://en.wikipedia.org/wiki/Finite-state_machine) in C. The states are implemented as function pointers which scale much better than implementations using switch/case construction. It also allows the compiler to check if a state is valid, which is not possible using enums or defines for states.

States

States are implemented as a function that will be called in loop as long as the machine stays in the same state.

Transitions

Transition from one state to another is simply handled by calling state_machine_set_current_state with the destination state as a parameter, then returning from the state function.

Example

Simple example of a state machine that can be used to match C++ style ("//") comments on text read from stdin.

#include <stdio.h>
#include "state_machine.h"

void state1(state_machine_t *machine);
void state2(state_machine_t *machine);

void main(void)
{
    state_machine_t *machine;
    machine = state_machine_create();
    state_machine_set_current_state(machine, state1);

    while (state_machine_state_is_valid(machine)) {
        state_machine_run(machine);
    }

    state_machine_delete(machine);
}

void state1(state_machine_t *machine)
{
    /* If we read '/' change state to state2, otherwise stay in state1. */
    if (getchar() == '/') {
        state_machine_set_current_state(machine, state2);
    }
}

void state2(state_machine_t *machine)
{
    if (getchar() == '/') {
        state_machine_exit(machine);
    } else {
        state_machine_set_current_state(machine, state1);
    }
}

Sanity checks

For the moment no sanity checking is performed, which means you can transition to a state made for another state machine.

Dependencies