👀 Views: 100 💬 Answers: 1 📅 Created: 2025-06-11

c state-machine function-pointers C

I just started working with I'm upgrading from an older version and Quick question that's been bugging me - I've been struggling with this for a few days now and could really use some help. I'm working on a personal project and I'm trying to implement a simple state machine in C using function pointers for each state. My goal is to have a finite state machine that transitions between states based on user input. However, I'm encountering unexpected behavior when transitioning between states. For instance, sometimes the current state seems to execute multiple times before switching to the next state. Here's a simplified version of my code: ```c #include <stdio.h> #include <stdlib.h> typedef struct StateMachine { void (*current_state)(); } StateMachine; void stateA() { printf("State A\n"); } void stateB() { printf("State B\n"); } void transition_to(StateMachine *sm, void (*new_state)()) { sm->current_state = new_state; sm->current_state(); // Execute current state immediately } int main() { StateMachine sm; sm.current_state = stateA; sm.current_state(); // Initial state transition_to(&sm, stateB); // Transition to state B transition_to(&sm, stateA); // Transition back to state A return 0; } ``` When I run this code, it outputs: ``` State A State B State A ``` Which is what I expected. However, if I modify the `transition_to` function to call the current state based on an input condition, like this: ```c void transition_to(StateMachine *sm, void (*new_state)(), int condition) { if (condition) { sm->current_state = new_state; } sm->current_state(); // Execute current state immediately } ``` And then call it like: ```c transition_to(&sm, stateB, 1); // Transition to state B transition_to(&sm, stateA, 0); // This should not change the state ``` I end up getting unexpected output where State A appears multiple times. It seems like the state is being executed even when I don't intend to transition. What am I missing in this design? How do I prevent the current state from executing if the transition condition is not met? For context: I'm using C on macOS. Thanks in advance! Am I missing something obvious? Has anyone else encountered this?