Question
Can someone please help me write a program in C for a Finite State Machine (FSM) that accepts all strings of input symbols that have an odd number of symbols. The alphabet of input symbols is {0,1}.
Explanation / Answer
/** * @file fsm.c * @brief an implementation for a FSM in C, this file contains * implementation of definations. * License GPLv3+ * @author Ankur Shrivastava */#include "fsm.h"#include#include/** * Function to initialize the FSM * @param obj pointer to structure of type fsm_object, which defines the FSM */int fsm_init(struct fsm_object *obj){ //initialize everything to Null or 0 obj->fsm_base = NULL; obj->fsm_cur_state_name = NULL; obj->fsm_arg_num = 0; obj->fsm_arg_value = NULL; return 0;}/** * Execution of next state takes place here * @details function fsm_next can be used without fsm_main when we want to hadel * state execution and not rely on fsm_main 's loop * @param obj pointer to structure of type fsm_object, which defines the FSM */int fsm_next_state(struct fsm_object *obj){ struct fsm_state *tmp = obj->fsm_base; if ((obj->fsm_base==NULL)||(obj->fsm_cur_state_name==NULL)) { return -1; } while ((tmp->name != obj->fsm_cur_state_name)&&(tmp!=NULL)) tmp = tmp->next; if (tmp == NULL) return -1; tmp->function(obj,obj->fsm_arg_num,obj->fsm_arg_value); return 0;}/** * The FSM entry point, this is where execution of code begins in FSM. * @param obj pointer to structure of type fsm_object, which defines the FSM */int fsm_main(struct fsm_object *obj){ while (!fsm_next_state(obj)); return 0;}/** * Function to add a new state to the FSM. * @param obj pointer to structure of type fsm_object, which defines the FSM * @param state name of the state to be added. * @param fun name of the function to be executed for this state */int fsm_add(struct fsm_object *obj, char *state, void (*fun)(struct fsm_object *, int ,void **) ){ struct fsm_state *tmp = obj->fsm_base; struct fsm_state *new_state = malloc(sizeof(struct fsm_state)); while(tmp->next) tmp = tmp->next; new_state->name = state; new_state->function = fun; new_state->next=NULL; tmp->next=new_state; return 0;}/** * Function to remove a state from the FSM. * @param obj pointer to structure of type fsm_object, which defines the FSM * @param state name of state to be removed */int fsm_remove(struct fsm_object *obj,char *state){ if (!strcmp(state,"default")) return -1; struct fsm_state *to_del; struct fsm_state *tmp=obj->fsm_base; while((tmp->next!=NULL)&&(strcmp(tmp->next->name,state))) tmp=tmp->next; if (tmp == NULL) return -1; to_del = tmp->next; tmp->next = tmp->next->next; free(to_del); return 0;}/** * Function to change state. * @details changes state to the new specified state, if the state does not exist returns error, * state change is not triggered till function calling fsm_to_state returns * @param obj pointer to structure of type fsm_object, which defines the FSM * @param state name of state to chnage to * @param num number of arguments * @param arg arguments */int fsm_to_state(struct fsm_object *obj, char *state, int num, void** arg){ struct fsm_state *tmp=obj->fsm_base; while((tmp!=NULL)&&(strcmp(tmp->name,state))) tmp=tmp->next; if (tmp == NULL) return -1; obj->fsm_cur_state = tmp; obj->fsm_cur_state_name = tmp->name; obj->fsm_arg_num = num; obj->fsm_arg_value=arg; return 0;}/** * Function to add a default state to FSM. * @details Adds a default state to FSM, this is the function called at the start of the FSM * or in case of error, with the appropriate error code * @param obj pointer to structure of type fsm_object, which defines the FSM * @param fun name of the function to be executed for this state */int fsm_default(struct fsm_object *obj, void (*fun)(struct fsm_object *, int ,void **) ){ obj->fsm_base = malloc(sizeof(struct fsm_state)); obj->fsm_base->name="default"; obj->fsm_base->function = fun; obj->fsm_base->next = NULL; // set current state to default obj->fsm_cur_state = obj->fsm_base; obj->fsm_cur_state_name = obj->fsm_base->name; return 0;}/** * Function for FSM termination * @param obj pointer to structure of type fsm_object, which defines the FSM */void fsm_terminate(struct fsm_object *obj){ // delete all states to prevent memory leek struct fsm_state *tmp = obj->fsm_base; struct fsm_state *to_del=tmp; while(tmp) { to_del = tmp; tmp=tmp->next; free(to_del); } // reset FSM base to NULL causes while loop in fsm_main to quit // terminating the program obj->fsm_cur_state = NULL; obj->fsm_cur_state_name = NULL; obj->fsm_base = NULL;}