Multiple arguments to function called by pthread create

Question

I need to pass multiple arguments to a function that I would like to call on a separate thread  I ve read that the typical way to do this is to define a struct  pass the function a pointer to that  and dereference it for the arguments  However  I am unable to get this to work    include  lt stdio h gt   include  lt pthread h gt   struct arg struct       int arg1      int arg2      void  print the arguments void  arguments        struct arg struct  args    struct arg struct   args      printf   d n   args - gt  arg1       printf   d n   args - gt  arg2       pthread exit NULL       return NULL     int main         pthread t some thread      struct arg struct args      args arg1   5      args arg2   7       if  pthread create  amp some thread  NULL   amp print the arguments   void    amp args     0            printf  Uh-oh  n            return -1             return pthread join some thread  NULL      Wait until thread is finished        The output for this should be   5 7   But when I run it I actually get   141921115 -1947974263   Anyone know what I m doing wrong

User · Answer

I have the same question as the original poster, Michael.

However I have tried to apply the answers submitted for the original code without success

After some trial and error, here is my version of the code that works (or at least works for me!). And if you look closely, you will note that it is different to the earlier solutions posted.

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

struct arg_struct
{
   int arg1;
   int arg2;
} *args;

void *print_the_arguments(void *arguments)
{
   struct arg_struct *args = arguments;
   printf("Thread\n");
   printf("%d\n", args->arg1);
   printf("%d\n", args->arg2);
   pthread_exit(NULL);
   return NULL;
}

int main()
{
   pthread_t some_thread;
   args = malloc(sizeof(struct arg_struct) * 1);

   args->arg1 = 5;
   args->arg2 = 7;

   printf("Before\n");
   printf("%d\n", args->arg1);
   printf("%d\n", args->arg2);
   printf("\n");


   if (pthread_create(&some_thread, NULL, &print_the_arguments, args) != 0)
   {
      printf("Uh-oh!\n");
      return -1;
   }

   return pthread_join(some_thread, NULL); /* Wait until thread is finished */
}

User · Answer

In this code s thread creation  the address of a function pointer is being passed  The original pthread create  amp some thread  NULL   amp print the arguments   void    amp args     0  It should read as pthread create  amp some thread  NULL  print the arguments   void     amp args   A good way to remember is that all of this function s arguments should be addresses   some thread is declared statically  so the address is sent properly using  amp    I would create a pthread attr t variable  then use pthread attr init   on it and pass that variable s address  But  passing a NULL pointer is valid as well   The  amp  in front of the function label is what is causing the issue here  The label used is already a void  to a function  so only the label is necessary   To say    0 with the final argument would seem to cause undetermined behavior  Adding this means that a boolean is being passed instead of a reference   Akash Agrawal s answer is also part of the solution to this code s problem

User · Answer

The args of print the arguments is arguments  so you should use   struct arg struct  args    struct arg struct   arguments

User · Answer

main   has it s own thread and stack variables  either allocate memory for  args  in the heap or make it global    struct arg struct       int arg1      int arg2   args     declares args as global out of main     Then of course change the references from args- gt arg1 to args arg1 etc

User · Answer

struct arg struct  args    struct arg struct   args    --  this assignment is wrong  I mean the variable argument should be used in this context  Cheers

User · Answer

Because you say   struct arg struct  args    struct arg struct   args    instead of   struct arg struct  args   arguments

User · Answer

use   struct arg struct  args    struct arg struct   arguments    in place of   struct arg struct  args    struct arg struct   args

User · Answer

Use   struct arg struct  args   malloc sizeof struct arg struct      And pass this arguments like this   pthread create  amp tr  NULL  print the arguments   void   args     Don t forget free args

User · Answer

Since asking the same question but for C   is considered a duplicate I might as well supply C   code as an answer      hello-2args cpp    https   stackoverflow com questions 1352749  include  lt iostream gt   include  lt omp h gt   include  lt pthread h gt  using namespace std   typedef struct thread arguments     int thrnr    char  msg    thargs t   void  print hello void  thrgs      cout  lt  lt    thargs t  thrgs - gt msg  lt  lt    thargs t  thrgs - gt thrnr  lt  lt   quot  n quot     pthread exit NULL      int main int argc  char  argv        cout  lt  lt   quot  Hello C    n quot     const int NR THRDS   omp get max threads      pthread t threads NR THRDS     thargs t thrgs NR THRDS     for int t 0 t lt NR THRDS t          thrgs t  thrnr   t      thrgs t  msg    char   quot Hello World  - It s me      thread   quot       cout  lt  lt   quot In main  creating thread  quot   lt  lt  t  lt  lt   quot  n quot       pthread create  amp threads t   NULL  print hello   amp thrgs t          for int t 0 t lt NR THRDS t          pthread join threads t   NULL         cout  lt  lt   quot After join  I am always last  Byebye  n quot     return EXIT SUCCESS     Compile and run by using one of the following  g   -fopenmp -pthread hello-2args cpp  amp  amp    a out   Linux g   -fopenmp -pthread hello-2args cpp  amp  amp    a exe   MSYS2  Windows

[c] Multiple arguments to function called by pthread_create()?

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