Error: " undefined reference to......."

[Ihtisham]

Hey guys, how to over come the error in the title?

[Zeillinger]

Well, you are probably referring to something that isn't defined in the scope (self explanatory). We can't help you further without the code that is causing the problem.

[Ihtisham]

Well, here is the code:

#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<pthread.h>


#define NUM_THREADS 6
void *thread_function(void *arg);
int main()
{
     int res;
     pthread_t a_thread[NUM_THREADS];
     void *thread_result;
     int lots_of_threads;
     for(lots_of_threads = 0; lots_of_threads < NUM_THREADS; lots_of_threads++) {
     res = pthread_create(&(a_thread[lots_of_threads]), NULL, thread_function,
     (void *)&lots_of_threads);
     if (res != 0)
     {
          perror("Thread creation failed");
          exit(EXIT_FAILURE);
     }
     sleep(1);
}
     printf(" Waiting for threads to finish...\n" );
for(lots_of_threads = NUM_THREADS - 1; lots_of_threads >= 0; lots_of_threads--)
{
     res = pthread_join(a_thread[lots_of_threads], &thread_result);
     if (res == 0)
     {
          printf("Picked up a thread\n");
     }
     else
     {
          perror("pthread_join failed");
     }
     }
          printf("All done\n");
          exit(EXIT_SUCCESS);
     }
void *thread_function(void *arg)
{
     int my_number = *(int *)arg;
     int rand_num;
     printf("thread_function is running. Argument was %d\n", my_number);
     rand_num=1+(int)(9.0*rand()/(RAND_MAX+1.0));
     sleep(rand_num);
     printf("Bye from %d\n", my_number);
     pthread_exit(NULL);
}

[anonymous23323124]

And to what is the undefined reference?

EDIT: If you don't know how to answer this, just copy & paste the precise compiler errors you are getting.