threads in c, how to use them to move a player?

Question

Update my code

So i am working on a 2d game in c, now i am using threads to do different stuff in the same time, to move the player, cars etc.

But somehow i don't get it how can i move my player just one step, i know that the problem lays in my global variable movement. But can figure it how to do it the right way. So i hope someone can help me.

The code is huge so i will not passt all of it but the parts that are interesting for the player movement.

void moveFroggy() {
    //    froggy.y = SCREEN_HEIGHT - OUTER_BORDER;
    if((movement == 'a') && (froggy.x > OUTER_BORDER))
        froggy.x--;
    if((movement == 'd') && (froggy.x < (SCREEN_WIDTH - OUTER_BORDER)))
        froggy.x++;
    if ((movement == 'w') && (froggy.y >= (SCREEN_HEIGHT - NUM_LANES - OUTER_BORDER - GRASS_BORDER)))
        froggy.y--;
    if ((movement == 's') && (froggy.y < (SCREEN_HEIGHT - OUTER_BORDER)))
        froggy.y++;
    if(movement == 'q')
        quit = 1;
    if(froggy.y <= (SCREEN_HEIGHT - NUM_LANES - OUTER_BORDER - GRASS_BORDER))
    player_won = 1;
    movement = '0';
    }

Now inside the main we have a while loop that runs all the time, till the player complete the game or quit it.

pthread_create(&input_t, NULL, input_runner, NULL);

while(!quit && !error && !player_lost && !player_won) {
    moveFroggy();
    moveCarsOnMotorway();
    startCar((SCREEN_WIDTH - OUTER_BORDER));
    drawScreen();
    usleep(GAME_SPEED);
}

pthread_join(input_t, NULL);

So my input_t thread is calling the input_runner function inside that function i get the user input.

void *input_runner(void* arg) {
  char input;
  if(!player_lost || !player_won){
    while((input = getchar()) != EOF){
     movement = input;
    }
  }
  pthread_exit(0);

}

Just to know movement is a global variable so i can use it for moveFroggy function. but that is the problem to because it stores "w" and it just repeat itself till the user hit any other command. But it should move the player just one step ahead, so how can i reset the value and how to do proper clean up for threads if one is needed.

I am new in using thread,

Answer 1

Well, it seems the simple way to only move one step would be, at the bottom of moveFroggy() to clear movement value.

As an aside, it looks like you're creating an input-processing thread on every iteration of your game loop; is that really what you intend? If you want an input-processing thread, why not have it run its own loop to constantly read input until the game is over?

I'm also not sure of this overall multithreading strategy, but perhaps it will work for you...

Answer 2

This is not a good use of threads, and will be prone to synchronization errors.

Variables that are accessed by multiple threads must be protected by a mutex or accessed using atomic methods. Failing to do so will result in unpredictable behavior.

In any case, you don't need threads for this. If you want to read from the keyboard without blocking, there are a number of ways of doing that , including:

• If on Linux, use the ncurses library, which natively provides non-blocking keyboard input through getch() .
• If on Windows, use kbhit() .
• Use fcntl() with F_SETFL to set standard input as non-blocking.
• Use select() or poll() to check for input before trying to read.
• Avoid the console entirely, and use a graphics library such as SDL.