[ILUG] threads compilation problem

[Mark Fallon]

john carter wrote:
> 
> hi
> when i compile the file below using gcc abthread.c I get the following type of errors .
> 
> /tmp/cc4WfL0U.o(.text+0x6b) undefined reference to pthread_create
> /tmp/cc4WfL0U.o(.text+0xd7) undefined reference to pthread_join
> 
> any ideas
> thanks john
> 
> heres the file
> 
> /* Creates two threads, one printing 10000 "a"s, the other printing
>    10000 "b"s.
>    Illustrates: thread creation, thread joining. */
> 
> #include <stddef.h>
> #include <stdio.h>
> #include <unistd.h>
> #include <pthread.h>
> 
> void * process(void * arg)
> {
>   int i;
>   fprintf(stderr, "Starting process %s\n", (char *) arg);
>   for (i = 0; i < 10000; i++) {
>     write(1, (char *) arg, 1);
>   }
>   return NULL;
> }
> 
> int main(void)
> {
>   int retcode;
>   pthread_t th_a, th_b;
>   void * retval;
> 
>   retcode = pthread_create(&th_a, NULL, process, (void *) "a");
>   if (retcode != 0) fprintf(stderr, "create a failed %d\n", retcode);
>   retcode = pthread_create(&th_b, NULL, process, (void *) "b");
>   if (retcode != 0) fprintf(stderr, "create b failed %d\n", retcode);
>   retcode = pthread_join(th_a, &retval);
>   if (retcode != 0) fprintf(stderr, "join a failed %d\n", retcode);
>   retcode = pthread_join(th_b, &retval);
>   if (retcode != 0) fprintf(stderr, "join b failed %d\n", retcode);
>   return 0;
> }
> 
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try add -lpthread to your compile line.
The reason you are getting undefined symbols is because
the linker can not find the thread functions in the list
of default libraries it includes.



Mark
-- 
_______________________________________________________________

Mark Fallon			E-mail : mfallon at ie.oracle.com
Senior Software Engineer	Phone  : +353-1-8033207
Product Line Engineering	Fax    : +353-1-8033221
_______________________________________________________________