Void Pointers Conversion in C

Question

I have a function that will return a void pointer. I need to cast it as a struct variable. For example, the struct is

struct book{
  char* name;
  int pages;
}

I already have assigned a local pointer to the struct, like this:

struct book* ptr;

The function returns a void pointer, and I need to cast it as a book pointer. Could I do this?

ptr = function_name(); //void pointer returned

Or would I have to "catch" the returned void pointer in a local void pointer, then convert that to ptr?

Thanks!

Did your compiler complain about the assignment? Or what causes your doubts? — UnholySheep, Oct 13 '18 at 21:44
Well, I know for a fact that I need to cast it as a book pointer. However, I'm also aware that I cannot simply assign the value as I did above. I'm just looking for the proper syntax to convert from void pointer to book pointer after the function call. — Manny Rodriguez, Oct 13 '18 at 21:47
The C standard says you can just assign it, what makes you think you cannot? — UnholySheep, Oct 13 '18 at 21:47
Refer this https://stackoverflow.com/questions/16986214/why-type-cast-a-void-pointer — shirish, Oct 13 '18 at 21:50
Hmm. Interesting. Ok, I will try just assigning it. I will let you know if it doesn't work! Thanks for your help! — Manny Rodriguez, Oct 13 '18 at 21:54
Why would you not have just tried it _before_ asking the question!? — Clifford, Oct 13 '18 at 22:08

shirish · Answer 1 · 2018-10-13T21:58:06.153

0

struct book{
  char* name;
  int pages;
};

A void* ptr does not need an explicit cast.(although for compatibility or compiler issues you might need to explicitly cast as
struct book* ptr = (struct book*)ptr = (struct book*)function_name();

struct book *ptr = function_name();

edited Oct 13 '18 at 21:58

answered Oct 13 '18 at 21:46

shirish

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4

That should not be necessary, a `void*` is implicitly convertible to a pointer of any other type – UnholySheep Oct 13 '18 at 21:47
3

No, [you don't cast the result of `malloc` in C](https://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc) – UnholySheep Oct 13 '18 at 21:48
It's an unnecessary cast. Just assign directly to `ptr`, no cast is required, nor should one be supplied. – jwdonahue Oct 13 '18 at 21:50
1

Which "compatibility or compiler issues"? Be explicit. – jwdonahue Oct 13 '18 at 23:04
Why this `... (struct book*)ptr ...`? – alk Oct 14 '18 at 08:23
Refer this https://stackoverflow.com/questions/10568301/why-does-the-compiler-complain-when-i-do-not-cast-the-result-of-malloc – shirish Oct 14 '18 at 08:56

Void Pointers Conversion in C

1 Answers1