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Old 01-28-2005, 06:11 AM   #1
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Registered: Jan 2005
Location: Athens
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Passing Arguments into the Thread Function


I try to write a simple program for creating threads in C++. If I don't have arguments in the Thread Function, it works fine. The problem arises when I try to pass an argument to this function. I have found various code examples, but they all cause compile errors. More specifically, the part of my code concerning the thread creation is the following:

#include <pthread.h>

struct two_args {
int arg1;
int arg2;

void *needs_2_args(void *);

pthread_t t;
struct two_args *ap;

ap = (struct two_args *) malloc(sizeof (struct two_args));
ap->arg1 = 1;
ap->arg2 = 2;
error = pthread_create(&t, NULL, needs_2_args, (void *) ap);
if (error != 0)
deal_with_error ();

void *
needs_2_args(void *ap)
struct two_args *argp = (void *) ap;
int a1, a2;

a1 = argp->arg1;
a2 = argp->arg2;

While compiling, I get the following error:

In function void* needs_2_args(void*)
invalid conversion from 'void*' to 'two_args*'

Similar compile response appears, even if I use a simple argument (e.g. int) and not a struct. As I said before, I have used many code examples from the internet, but they are all similar and I get the same output.

The compiling part of my Makefile is the following:
g++ -c -o $(LIB_DIR)/Test.o -l $(INC_LIB) $(SRC_DIR)/Test.cpp

Do I forget an option? I am using also -lpthread but in the linking part. Should I use it also in the compiling part? If yes, in which place?

Please note that I don't have any experience in Linux Programming.

Thanks in advance,
Old 01-28-2005, 04:15 PM   #2
Registered: Feb 2002
Location: Grenoble
Distribution: Debian
Posts: 9,575

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Re: Passing Arguments into the Thread Function

void * 
needs_2_args(void *ap) 
  struct two_args *argp = (struct two_args *) ap; 
  int a1, a2; 

  a1 = argp->arg1; 
  a2 = argp->arg2; 
I think it should be this way.
Old 01-31-2005, 06:03 AM   #3
LQ Newbie
Registered: Jan 2005
Location: Athens
Posts: 11

Original Poster
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Thanks a lot Mara, it is working now.


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