Passing and accessing multiple parameters to pthread function

Question

I am a beginner to cpp and threads. Referred to some code snippets in stackoverflow to pass multiple arguments to a pthread function and came up with the below code. I am not sure how to access the struct members inside the function using (void*) pointer passed to it. Can anyone explain?

#include <iostream>
#include <pthread.h>
#include <vector>
using namespace std;

struct a{
vector <int> v1;
int val;
};

void* function(void *args)
{
 vector <int>functionvector = (vector <int>)args->v1;
 functionvector.push_back(args->val);
 return NULL;
}


int main()
{
  pthread_t thread;
  struct a args;

  pthread_create(&thread, NULL, &function, (void *)&args);
  pthread_join(thread,NULL);
  for(auto it : args.v1)
  {
    cout<<it;
   }

  return 0;
}

Getting the error : error: ‘void*’ is not a pointer-to-object type

You must cast back to the type you casted from. &args is an a*. — molbdnilo
– molbdnilo, Commented Nov 27, 2017 at 12:56

Bo Persson · Accepted Answer · 2017-11-27 12:58:25Z

1

You cannot access the members of a until you have cast the void* back to an a*.

void* function(void *ptr)
{
 a* args = static_cast<a*>(ptr);

 args->v1.push_back(args->val);
 return NULL;
}

answered Nov 27, 2017 at 12:58

Bo Persson

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1 Comment

newbie Over a year ago

Oops! Got it! Thanks.

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