Warning: cast to/from pointer from/to integer of different size

Question

I\'m learning Pthreads. My code executes the way I want it to, I\'m able to use it. But it gives me a warning on compilation.

I compile using:

gcc          


        

Answer 1

I was also getting the same warning. So to resolve my warning I converted int to long and then this warning just vanished. And about the warning "cast to pointer from integer of different size" you can leave this warning because a pointer can hold the value of any variable because pointer in 64x is of 64 bit and in 32x is of 32 bit.

Answer 2

pthread_create(&(tid[i]), &attr, runner, (void *) i);

You are passing the local variable i as an argument for runner, sizeof(void*) == 8 and sizeof(int) == 4 (64 bits).

If you want to pass i, you should wrap it as a pointer or something:

void *runner(void * param) {
  int id = *((int*)param);
  delete param;
}

int tid = new int; *tid = i;
pthread_create(&(tid[i]), &attr, runner, tid);

You may just want i, and in that case, the following should be safe (but far from recommended):

void *runner(void * param) {
  int id = (int)param;
}

pthread_create(&(tid[i]), &attr, runner, (void*)(unsigned long long)(i));

Answer 3

A quick hacky fix might just to cast to long instead of int. On a lot of systems, sizeof(long) == sizeof(void *).

A better idea might be to use intptr_t.

int threadnumber = (intptr_t) param;

and

pthread_create(&(tid[i]), &attr, runner, (void *)(intptr_t)i);

Answer 4

Try passing

pthread_create(&(tid[i]), &attr, runner, (void*)&i);