how can i cast void* to int correctly?

Question

When I'm studying C, I find this program:

#include<stdio.h>
struct Base
{
void* data;
}
int main()
{
struct Base* base = (struct Base*)malloc(sizeof(struct Base));
if(!base) return -1;
int value = 90;
base->data = value;
printf("%d", base->data);
return 0;
}

When compiling, output "warning: assignment to void* from int makes pointer from integer without a cast" How can I solve this problem?

That's not a program you have, it does not compile because you're missing a semicolon. — Antti Haapala -- Слава Україні, Mar 24 '21 at 14:23
Also there is no solving the problem without you telling what needs to be done. But in this case the most sensible thing is to have `int data;` instead of `void *data`. Also never cast the return value of `malloc` -you're missing `#include ` and hence your program is very much broken. — Antti Haapala -- Слава Україні, Mar 24 '21 at 14:24
copy paste the exact code that you're compiling when posting questions — klutt, Mar 24 '21 at 14:26
What you are doing makes no sense. An `int` is not a `void *`, and attempting to assign an integer value to a `void *` is a disaster waiting to happen. 30 years ago, it was common to treat pointers as if they were integers, and it led to countless programming errors. Stop perpetuating a decade's old bad practice. — William Pursell, Mar 24 '21 at 14:33

klutt · Answer 1 · 2021-03-24T14:34:36.280

2

This will solve it. data is a pointer, so you need to assign it to the address of the variable:

base->data = &value;
printf("%d", *(int*)base->data);

If you really mean what you're writing, but just want to get rid of the warning, use this:

base->data = (void*)value;

But if you're doing that, it's a good sign you're doing something wrong.

Other than that, Don't cast malloc

edited Mar 24 '21 at 14:34

answered Mar 24 '21 at 14:28

klutt

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I suppose it's possible, though unlikely, OP is using the address of `data` as the `int` value. `base->data = (void *)value`; `value = (int)(base->data)`. – Fiddling Bits Mar 24 '21 at 14:30

how can i cast void* to int correctly?

1 Answers1