How Can I Efficiently Implement State Machines in C Using Tried-and-Tested Techniques?

C State-Machine Design: Tried-and-Tested Implementation Techniques

In this discussion, we explore tried-and-tested techniques for designing state machines in C.

Struct Array and Loop Approach

A common approach involves using an array of structures to represent the state machine. Each structure contains the current state, event, and a function that calculates the next state.

typedef struct {
    int st;
    int ev;
    int (*fn)(void);
} tTransition;

Event-Driven Operation

The state machine operates by handling events. The event loop continuously checks for events and looks up the corresponding transition in the transition array.

while (state != ST_TERM) {
    event = GetNextEvent();
    for (i = 0; i < TRANS_COUNT; i++) {
        if ((state == trans[i].st) || (ST_ANY == trans[i].st)) {
            if ((event == trans[i].ev) || (EV_ANY == trans[i].ev)) {
                state = (trans[i].fn)();
                break;
            }
        }
    }
}

Wildcards for Flexibility

Wildcards (ST_ANY and EV_ANY) can be used to handle events that are valid in any state or at any event.

Passing a Structure for Multiple Machines

To avoid global variables for multiple state machines, a structure pointer can be passed to all functions, allowing each machine to maintain its own state.

Conclusion

These techniques provide a solid foundation for designing efficient and maintainable state machines in C. However, it's important to consider the specific requirements of each project and explore additional resources and advanced techniques as needed.

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