pthread_create - error when compiling in c

Question

When I try to compile this I get an error:

warning: passing argument 1 of pthread_create makes pointer from integer without a cast.

Please if anyone can help me..

    int Traveler(int id, int numBags)
    {
           int i;
           int err;
         err = pthread_create(id, NULL, Traveler, NULL);
         if(err!=0)
         {
                      return -1;
         }
         else
         {

         }
    }

smocking · Accepted Answer · 2012-04-24 17:14:36Z

4

The error is pretty clear. The first argument should be a pointer rather than an integer.

man pthread:

   int pthread_create(pthread_t *restrict thread,
          const pthread_attr_t *restrict attr,
          void *(*start_routine)(void*), void *restrict arg);

   The  pthread_create()  function  shall  create  a  new   thread,   with
   attributes  specified  by  attr, within a process. If attr is NULL, the
   default attributes shall be used. If the attributes specified  by  attr
   are modified later, the thread's attributes shall not be affected. Upon
   successful completion, pthread_create() shall store the ID of the  cre-
   ated thread in the location referenced by thread.

Re-read that last sentence before sticking an ampersand before id in your pthread_create call. EDIT2: you will also have to define id as a pthread_t.

EDIT:

Actually, there are two other issues on the same line: start_routine needs to be a function that takes one argument rather than two, but worst of all this would be a fork bomb since you're passing the same function you're calling from!

edited Apr 24, 2012 at 17:14

answered Apr 24, 2012 at 16:05

smocking

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2 Comments

Michael Burr Over a year ago

+1, but sticking an & in front of id isn't the right thing to do - the first argument needs to be a pointer to a pthread_t not a pointer to an int. The compiler might accept it (if pthread_t happens to be a typedef for an int), but not in general.

smocking Over a year ago

Good catch. Have updated my answer. Well, I guess that makes 4 errors in one line... :-)

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