Why am I getting this error? void * is not a pointer to an object type.

Question

void *stackAddr[NUM_THREADS];

stackAddr[i] = malloc(STACKSIZE);

The compiler (g ++ 4.4.3) complains where malloc is called ...

warning: pointer of type ‘void *’ used in arithmetic
error: ‘void*’ is not a pointer-to-object type

If you are interested in seeing all the code, here it is ...

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define NUM_THREADS 4

void *stackAddr[NUM_THREADS];
pthread_t thread[NUM_THREADS];
pthread_attr_t attr;

void *BusyWork(void *t)
{
   int i;
   long tid;
   double result=0.0;
   tid = (long)t;

   printf("Thread %ld starting...\n",tid);
   for ( i = 0; i < 1000; i++)
   {
      result = result + sin(i*tid) * tan(i*tid);
   }
   printf("Thread %ld done. Result = %e\n", tid, result);
   pthread_exit((void*) t);
}

void pthread_create_with_stack( pthread_t * pthread, void *(*start_routine) (void *), int tid )
{
    const size_t STACKSIZE = 0xC00000; //12582912
    void *stackAddr;
    int rc;
    size_t i;
    pthread_t thread;
    pid_t pid;

    stackAddr[tid] = malloc(STACKSIZE); // Error here!
    pthread_attr_setstack(&attr, stackAddr[tid], STACKSIZE);

    rc = pthread_create( pthread, &attr, start_routine, (void*)tid );
}

int main (int argc, char *argv[])
{
   int rc;
   long t;
   void *status;

   /* Initialize and set thread detached attribute */
   pthread_attr_init(&attr);
   pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

   for(t=0; t<NUM_THREADS; t++) 
   {
      printf("Main: creating thread %ld\n", t);
      rc = pthread_create_with_stack(&thread[t], BusyWork, t); 
      if (rc) 
      {
         printf("ERROR; return code from pthread_create() is %d\n", rc);
         exit(-1);
      }
   }

   /* Free attribute and wait for the other threads */
   pthread_attr_destroy(&attr);
   for(t=0; t<NUM_THREADS; t++) 
   {
      rc = pthread_join(thread[t], &status);
      if (rc) 
      {
         printf("ERROR; return code from pthread_join() is %d\n", rc);
         exit(-1);
      }
      printf("Main: completed join with thread %ld having a status"   
            "of %ld\n",t,(long)status);
    }

    printf("Main: program completed. Exiting.\n");
    pthread_exit(NULL);
}

Answer 1

You declare a local variable void *stackAddrthat obscures the global array stackAddr.

In addition, it is not an array, and the use of the index operator []tries to shift and dereference the pointer void, therefore, to compile the error.

Separation and arithmetic pointer to void pointers are not permitted by the standard, as they sizeof(void)are undefined.

Answer 2

:

void *stackAddr;

:

void *stackAddr[];

( .)

:

stackAddr[tid] = malloc(STACKSIZE);

, void*.

Answer 3

, , pthread_create_with_stack, void * stackAddr, .

, .

Answer 4

, , .

void *stackAddr[NUM_THREADS];

- :

void *stackAddr;

, , .

Answer 5

pthread_create_with_stack :

void *stackAddr;
...
stackAddr[tid] = malloc(STACKSIZE)

stackAddr[tid] a void*.

Answer 6

stackAddr , stackAddr[tid]. *(stackAddr + tid) , stackAddr + tid * sizeof(void), sizeof(void).

Answer 7

++ void , . i- . .