Question

I’m having a problem with my C code where I declare a static int variable (as a flag), then initialize it to -1 in init() which is only called once, then when I try to update the value to 0 or 1 later on, it keeps reverting back to -1.

Does anyone know what the problem can be?

I don’t have any local variables with the same identifier so I’m really lost.

Thanks!

static int previousState;

void init()
{
   previousState = -1;
}

void moveForward(int currentState)
{
    if (previousState == -1)
        previousState = currentState;

    if (previousState != currentState)
    {
        /* do stuff */
        /* PROBLEM: it never goes into here, because previousState is always -1! */
    }

    /* other code */
}

void main()
{
   init();

   if (fork() == 0)
   {
        /* do stuff */
        moveForward(1);
        exit();
   }

   /* more forks */

   moveForward(0);
   exit();
}

Answer 1

Each process calls moveForward just once. Processes do not share static data!

Use threads, or use shared memory. Also use mutex or semaphore for concurrent access of shared data . Preferably switch to a language better suited for parallel prosessing…