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# 1  
Old 06-13-2012
void pointer
hi guys!

Is there such a thing as double void pointer dynamic allocation?
And if so is it something like this?

Code:
int n;
void** a;
a=malloc(n*sizeof(void*));

# 2  
Old 06-13-2012
The void does datatype does not have a size, so that will not work. Yes, void ** can exist.

What are you trying to accomplish?
# 3  
Old 06-13-2012
Quote:
Originally Posted by jim mcnamara
The void does datatype does not have a size, so that will not work. Yes, void ** can exist.

What are you trying to accomplish?
I want to have n void*.
But n is an argument to the function,that's why I thought it would be better if I had an array of void*
# 4  
Old 06-13-2012
The size of void may be undefined(not always -- sometimes it's '1' for the sake of easy pointer math), but the size of void * is definitely defined -- it's the same size as any other pointer.

I don't see any reason you couldn't have an array of void * pointers, and don't see anything wrong with the code you posted..
# 5  
Old 06-13-2012
Quote:
Originally Posted by Corona688
The size of void may be undefined(not always -- sometimes it's '1' for the sake of easy pointer math), but the size of void * is definitely defined -- it's the same size as any other pointer.

I don't see any reason you couldn't have an array of void * pointers, and don't see anything wrong with the code you posted..
The thing is that when I try to refer to one element of the array,that means to one void* it doesn't work.
For example when I had:

Code:
main(){
    void* a;
    fun(&a); //call a function named fun
}

void fun(void** b){
//do things
}

it worked fine.But when I did this for many void* in a loop

Code:
main(){
   void** a;
   a=(void**)malloc(n*sizeof(void*));
   for(int i=0;i<n;i++)
      fun(a[i]);//call the same function as above
}

void fun(void **b){
  //do things
}

it returns segmentation fault.
# 6  
Old 06-13-2012
Quote:
Originally Posted by vlm
it worked fine.But when I did this for many void* in a loop

Code:
main(){
   void** a;
   a=(void**)malloc(n*sizeof(void*));
   for(int i=0;i<n;i++)
      fun(a[i]);//call the same function as above
}

void fun(void **b){
  //do things
}

it returns segmentation fault.
Dont know what code is inside fun but you cant dereference a void*...besides a[i] is a void* not void** so definition of fun needs to change to "void fun(void *b) {...}"
This User Gave Thanks to shamrock For This Post:
vlm
# 7  
Old 06-14-2012
Quote:
Originally Posted by shamrock
Dont know what code is inside fun but you cant dereference a void*...besides a[i] is a void* not void** so definition of fun needs to change to "void fun(void *b) {...}"
Actually I changed the
Code:
a[i]

to
Code:
&a[i]

and works fine.
One more question,if I want to send in a function not only one element:
Code:
&a[i]

but all of them do I simply do:

Code:
funct(a);//a is the void**

and if so ,the function's argument is:

Code:
void funct(void** a){
   int cc;
   for(int i=0;i<n;i++)
      memcpy(&cc,*a[i]+sizeof(int),sizeof(int));//and this is how we reffer to each void* pointer of the group?

}
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