I have a structure named graph.

graph *G;

Now I create memory of size of structure using malloc and the start pointer is stored in pointer G.

G = (graph*)malloc(sizeof(graph));

My question is how do I pass this as a argument to pthread_create?

pthread_create(&th,NULL,function_call, ? );

closed as off-topic by yannis Mar 18 '15 at 7:45

  • This question does not appear to be about software engineering within the scope defined in the help center.
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  • Are you sure you don't mean C rather than C++? – outis Mar 18 '15 at 5:30
  • 1
    Also, this is more of an implementation question than a design question, so should be asked on SO. – outis Mar 18 '15 at 5:35
  • Ya but then since I have posted it here already.. Why not answer it? – Nandini Singhal Mar 18 '15 at 5:39
  • just like in a previous question, I wonder, are you by chance blocked at Stack Overflow – gnat Mar 18 '15 at 7:15
  • 1
    This question does not appear to be about software development within the scope defined in the help center. – yannis Mar 18 '15 at 7:45

the prototype of pthread_create is

 int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
                          void *(*start_routine) (void *), void *arg);

As the arg parameter is a void* you can simply write

pthread_create(&th,NULL,function_call, G);

However, it the function_call(), you will need to cast you arg parameter to the real type. either:

function_call(void *arg)
    graph *tmp_G;

    tmp_G = arg;
    //  then I use tmp_G as G


((graph *)arg)->the_field_of_G;

Then you will be able to use you parameter as you need.

If you want to give more then one parameter to you function, you simply have to create a new structure that will contain all your parameters, then cast it as above to use them in your function_call().

here is an example :

typedef struct s_my_function_call_arg
    graph *G;
    int   arg2;
    char  *arg3;
}              t_my_function_call_arg;
  • ssca2.cpp: In function ‘int main(int, char**)’: ssca2.cpp:169:63: error: invalid conversion from ‘void ()(void)’ to ‘void* ()(void)’ [-fpermissive] rc = pthread_create(&threads[count], NULL,genScalData,G); ^ In file included from ssca2.cpp:79:0: /usr/include/pthread.h:244:12: error: initializing argument 3 of ‘int pthread_create(pthread_t*, const pthread_attr_t*, void* ()(void), void*)’ [-fpermissive] extern int pthread_create (pthread_t *__restrict __newthread, ^ – Nandini Singhal Mar 18 '15 at 9:18
  • The answer is writtend in your compilation error messages : invalid conversion from ‘void ()(void)’ to ‘void* ()(void). The return value of genScalData is suppose to be void *. – Bernard Jesop Mar 18 '15 at 9:26

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