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What is meant by FSM in c and what are the uses?

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What is meant by FSM in c and what is the uses and where we are using can anyone explain with an Example?

posted Oct 22, 2013 by Giri Prasad

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1 Answer

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FSM stands for Finite State Machine, it has no relation with C rather it has more generic meaning which is a State Machine which has finite number of states.

A state is a description of the status of a system that is waiting to execute a transition. A transition is a set of actions to be executed when a condition is fulfilled or when an event is received. In some finite-state machine representations, it is also possible to associate actions with a state:
Entry action: performed when entering the state,
Exit action: performed when exiting the state.

See the following sample (simple) state machine

typedef void transition_func_t( instance_data_t *data );

void do_initial_to_foo( instance_data_t *data );
void do_foo_to_bar( instance_data_t *data );
void do_bar_to_initial( instance_data_t *data );
void do_bar_to_foo( instance_data_t *data );
void do_bar_to_bar( instance_data_t *data );

transition_func_t * const transition_table[ NUM_STATES ][ NUM_STATES ] = {
    { NULL,              do_initial_to_foo, NULL },
    { NULL,              NULL,              do_foo_to_bar },
    { do_bar_to_initial, do_bar_to_foo,     do_bar_to_bar }

state_t run_state( state_t cur_state, instance_data_t *data ) {
    state_t new_state = state_table[ cur_state ]( data );
    transition_func_t *transition =
               transition_table[ cur_state ][ new_state ];

    if ( transition ) {
        transition( data );

    return new_state;
answer Oct 22, 2013 by Bob Wise