• State Not Answered
  • Locked Locked
  • Replies 10 replies
  • Subscribers 21 subscribers
  • Views 30641 views
  • Users 0 members are here
2025 survey

We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.

Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

void pointer to struct pointer cast

Victor Yokota

I declared a void pointer

void *ptr;

and a typedef struct named testStructure, with a member 'unsigned int a'.

Now I will cast this pointer to a struct pointer:

ptr=(testStructure*)malloc(sizeof(testStructure));

Now I try to access the member of the struct...

ptr->a=5;

...and I get an error "expression must have a pointer-to-struct-or-union type"...
Why is 'ptr' still void? It seems, a void pointer cannot be casted to any other pointer type...
How I can do this properly?
I just need ONE pointer, which can point to different structures, that means, I need to cast a void pointer...

Parents
  • 0 in reply to Frank Hali

    You have 2 conflicting goals.
    The kernel accessing data, and you not wanting to have an understanding of what it is accessing because it is in a DLL. If the Kernel merely needs to pass the data (pointer) I suppose this works.

    Erstwhile making a macro is likely the 'cleanest' route.
    IE

    typedef struct insect
{
 float value;
 char *name;
 uint32_t count;
}
insect;

#define INSECT(VPTR) ((insect *)(VPTR))
#define INSECT_VALUE(VPTR) INSECT(VPTR)->value
#define INSECT_NAME(VPTR)  INSECT(VPTR)->name
#define INSECT_COUNT(VPTR) INSECT(VPTR)->count

    etc

Reply
  • 0 in reply to Frank Hali

    You have 2 conflicting goals.
    The kernel accessing data, and you not wanting to have an understanding of what it is accessing because it is in a DLL. If the Kernel merely needs to pass the data (pointer) I suppose this works.

    Erstwhile making a macro is likely the 'cleanest' route.
    IE

    typedef struct insect
{
 float value;
 char *name;
 uint32_t count;
}
insect;

#define INSECT(VPTR) ((insect *)(VPTR))
#define INSECT_VALUE(VPTR) INSECT(VPTR)->value
#define INSECT_NAME(VPTR)  INSECT(VPTR)->name
#define INSECT_COUNT(VPTR) INSECT(VPTR)->count

    etc

Children