Pthreads - why C functions are declared as void*?

Question

Example ( source ):

#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS     5

void *PrintHello(void *threadid)
{
   long tid;
   tid = (long)threadid;
   printf("Hello World! It's me, thread #%ld!\n", tid);
   pthread_exit(NULL);
}

The function is declared to return a void pointer, but there's no return statement in its body. What is going on here?

Generally if a function has been declared as returning a value (in this case, a void pointer) and there's no return statement, its behaviour is undefined. Comments say that pthread_exit(NULL) is equivalent for calling return NULL - how can it be? You can call function B() from A() in such a way that B() calls return for A . Return statements refer to the function in which they are placed.

Answer 1

We can only speculate about what may be going on, but since it looks like a "Hello, World!" program, a reasonable guess would be that a pointer to that function is intended to be passed to pthread_create() . pthread_create() requires a pointer to a function having that signature. It's a strange construction even so; it would be equivalent but clearer for the function to just return NULL .