pthread_setname_np.3: EXAMPLES: remove a bug by simplify the code

From an email conversation with Alexis:

Hello Alexis,

On 8/6/21 7:06 PM, Alexis Wilke wrote:
> Hi guys,
>
> The pthread_setname_np(3) manual page has an example where the second
> argument is used to get a size of the thread name.
>
> https://man7.org/linux/man-pages/man3/pthread_setname_np.3.html#EXAMPLES
>
> The current code:
>
>            rc = pthread_getname_np(thread, thread_name,
>                                    (argc > 2) ? atoi(argv[1]) : NAMELEN);
>
> The suggested code:
>
>            rc = pthread_getname_np(thread, thread_name,
>                                    (argc > 2) ? atoi(argv[2]) : NAMELEN);

I agree that there's a problem, but I think we could go even simpler:

     rc = pthread_getname_np(thread, thread_name, NAMELEN);

> I'm thinking that maybe the author meant to compute the length like so:
>
>            rc = pthread_getname_np(thread, thread_name,
>                                    (argc > 2) ? strlen(argv[1]) + 1 :
> NAMELEN);
>
> But I think that the atoi() points to using argv[2] as a number
> representing the length.
>
> (Of course, it should be tested against NAMELEN as a maximum, but I
> understand that examples do not always show how to verify each possible
> error).

I imagine that the author's intention was to allow the user to do
experiments where argv[2] specified a number less than NAMELEN,
in order to see the resulting ERANGE error. But, that experiment
is of limited value, and complicates the code unnecessarily, IMO,
so that's why I made the change above.

--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

Reported-by: Alexis Wilke <alexis@m2osw.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/pthread_setname_np.3

@@ -201,8 +201,7 @@ main(int argc, char *argv[])
 
     sleep(2);
 
-    rc = pthread_getname_np(thread, thread_name,
-                            (argc > 2) ? atoi(argv[1]) : NAMELEN);
+    rc = pthread_getname_np(thread, thread_name, NAMELEN);
     if (rc != 0)
         errExitEN(rc, "pthread_getname_np");
     printf("The thread name after setting it is %s.\en", thread_name);