Best way to pass a struct within a struct to a GSourceFunc

Question

Which way is best to get S to a GSourceFunc? Or neither?

typedef struct{
//...
}S;

struct MS{
//..
S *St;
};

static gboolean AL_Calback(gpointer data){
    S *St = (S*)user_data;
    St->Something = SomethingElse;
    return TRUE;
} 

int main (int argc, char *argv[]){

    //...
    MS *MainStruct = gnew0(MS, 1);
    Mainstruct->St = gnew0(S, 1);
    clutter_threads_add_timeout_full(G_PRIORITY_HIGH, 100, AL_Callback, MainStruct->St, NULL); 
    //...
    }

or like this,

typedef struct{
//...
}S;

struct MS{
//..
S St;
};

static gboolean AL_Calback(gpointer data){
    MS *MV = (MS*)user_data;
    MV->S.something = SomethingElse;    
    return TRUE;
} 

int main (int argc, char *argv[]){

    //...
    MS *MainStruct = gnew0(MS, 1);
    clutter_threads_add_timeout_full(G_PRIORITY_HIGH, 100, AL_Callback, MainStruct, NULL); 
    //...
    }

I've tried other ways, but have not been able to make them work. clutter_add_timeout needs to take a pointer as an argument.

Attila · Accepted Answer · 2012-06-10T14:05:30.873

1

If you are passing the parameter to clutter_threads_add_timeout_Full via pointer, then you could just pass the address of the St member of MainStruct thus reducing the need for dynamic allocation (for the inner structure).

struct MainStruct{
  //..
  S St; // note: no pointer
};

// in main
MainStruct* ms = gnew0(MS, 1);
clutter_threads_add_timeout_Full(G_PRIORITY_HIGH, 100, AL_Callback, &(ms->St),
    NULL);

Edit: updated code to dynamically allocate MainStruct structure to avoid possible segfault as pointed out by ptomato

edited Jun 10 '12 at 14:05

answered Jun 07 '12 at 19:11

Attila

28,265
3
46
55

`clutter_threads_add_timeout` won't seam to let me pass anything but a gpointer, which is really just `(void*)`. – MVTC Jun 08 '12 at 07:05
@MVTCplusplus - then just ignore the sentence after the code. There is no difference between a) having a pointer member and passing that; and b) having a struct member and passing its address (except for memory allocation differences) – Attila Jun 08 '12 at 11:29
Thanks. I still haven't done any tests, but I think you pretty much answered my question. – MVTC Jun 08 '12 at 18:56
1

@Attila, your code runs the risk of the callback running after `ms` goes out of scope, thereby causing a segfault. – ptomato Jun 10 '12 at 13:49

Best way to pass a struct within a struct to a GSourceFunc

1 Answers1