A simple thread code.

gcc thread.c -DREENTRANT -L/usr/lib/nptl -lpthread -o thread

#include stdio.h
#include unistd.h
#include stdlib.h
#include string.h
#include pthread.h

void *thread_function(void * arg);

char message[] = "Hello world!";

int main()
{
int res;
pthread_t a_thread;
void *thread_result;

res = pthread_create(&a_thread , NULL , thread_function , (void*) message);
if(res != 0)
{
printf("Thread creation failed!\n");
}
printf("Waiting for thread to finish!\n");
res = pthread_join(a_thread, &thread_result);
if(res != 0)
{
printf("Thread join failed!\n");
}
printf("Thread joined! It returned %s\n",(char*)thread_result);
printf("Message is now %s\n",message);

}

void *thread_function(void *arg)
{
printf("Thread function is running . Argument was %s\n",(char *)arg);
sleep(10);
strcpy(message , "Bye!");
pthread_exit("Thank you for the CPU time!\n");
}