[SOLVED] how to pass integer value through pthread_create - C++

The correct way to retrieve the passed parameter follows

void *smoker_tobacco (void *id)
{
  long tid = (long)id;
  cout << "Thread id:"<< tid << endl;
  return (void *) 0;
}

Try, for instance

#include <iostream>
#include <pthread.h>
#include <semaphore.h>
using namespace std;


void *smoker_tobacco (void *id)
{
  long tid = (long)id;
  cout << "Thread id:"<< tid << endl;
  return (void *) 0;
}


int main()
{
  pthread_t smoker1,smoker4;
  sem_t table, sem_tobacco, sem_paper, sem_match;

  sem_init(&table,0,1);
  sem_init(&sem_tobacco,0,0);
  sem_init(&sem_paper,0,0);
  sem_init(&sem_match,0,0);

  pthread_create(&smoker1, NULL, smoker_tobacco, (void*)1);
  pthread_create(&smoker4, NULL, smoker_tobacco, (void*)4);

  cout<<smoker1<<","<<smoker4<<endl;

  pthread_join(smoker1,NULL);
  pthread_join(smoker4,NULL);

  return 0;
}

You can cast from int to void* and back again, without any problems:

#include <iostream>

void f(void *p)
{
    int i = reinterpret_cast<intptr_t>(p);
    std::cout << "f: i = " << i << '\n';
}

int main()
{
    f( reinterpret_cast<void*>(1) );

    return 0;
}

Note that this when going from void* to int we have to cast the pointer to inptr_t, otherwise, in 64 bit mode we get an error message regarding the cast from void* to int looses precision.
In this case, this is reasonably safe, since we know that sizeof(void*) >= sizeof(int), so any int can be represented in a void*.