有没有典型的状态机实现模式? [英] Is there a typical state machine implementation pattern?

问题描述

我们需要在 C 中实现一个简单的状态机.
标准的 switch 语句是最好的方法吗?
我们有一个当前状态(state)和一个转换触发器.

We need to implement a simple state machine in C.
Is a standard switch statement the best way to go?
We have a current state (state) and a trigger for the transition.

switch(state)
{
  case STATE_1:
     state = DoState1(transition);
     break;
  case STATE_2:
     state = DoState2(transition);
     break;
}
...
DoState2(int transition)
{
   // Do State Work
   ...
   if(transition == FROM_STATE_2) {
     // New state when doing STATE 2 -> STATE 2
   }
   if(transition == FROM_STATE_1) {
    // New State when moving STATE 1 -> STATE 2
   }
   return new_state;
}

是否有更好的方法用于简单状态机

对于 C++，我认为 Boost Statechart 库可能是要走的路.但是，它对 C 没有帮助没有.让我们专注于 C 用例.

For C++, I think the Boost Statechart library might be the way to go. However, it does not help with C. Lets concentrate on the C use case.

推荐答案

对于大多数状态机，我更喜欢使用表驱动的方法:

I prefer to use a table driven approach for most state machines:

typedef enum { STATE_INITIAL, STATE_FOO, STATE_BAR, NUM_STATES } state_t;
typedef struct instance_data instance_data_t;
typedef state_t state_func_t( instance_data_t *data );

state_t do_state_initial( instance_data_t *data );
state_t do_state_foo( instance_data_t *data );
state_t do_state_bar( instance_data_t *data );

state_func_t* const state_table[ NUM_STATES ] = {
    do_state_initial, do_state_foo, do_state_bar
};

state_t run_state( state_t cur_state, instance_data_t *data ) {
    return state_table[ cur_state ]( data );
};

int main( void ) {
    state_t cur_state = STATE_INITIAL;
    instance_data_t data;

    while ( 1 ) {
        cur_state = run_state( cur_state, &data );

        // do other program logic, run other state machines, etc
    }
}

这当然可以扩展到支持多个状态机等.也可以适应转换操作:

This can of course be extended to support multiple state machines, etc. Transition actions can be accommodated as well:

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;
};

表格驱动的方法更容易维护和扩展，更容易映射到状态图.

The table driven approach is easier to maintain and extend and simpler to map to state diagrams.

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