Can void pointers be dereferenced?

[rahul sinha]

#include<stdio.h>
#include<conio.h>

void main()

{
void *ptr;
char *a='A';
char *b="TAN";
int i=50;
ptr=a;
ptr=(char*)malloc(sizeof(a));
printf("%c",*ptr);
ptr=i;
ptr=(int*)malloc(sizeof(i));
printf("%d",++(*ptr));
ptr=b;
ptr=(char*)malloc(sizeof(b));
printf("%c",++(*ptr));
getch();
}

On compilation error, was we cant derefrence the void pointer but avoid pointer can point to any other pointer type. So after we have assigned a void pointer to say a pointer of type int, then we should be able to dereference the pointer no? I am not able to get this behavior.

[donbock]

The compiler does not know the type of what the void pointer points at, thus you can't dereference a void pointer. C does not support variant data types (where the type of the item is determined at run time).

What are you trying to accomplish?

[rahul sinha]

hey donbock i got it now that compiler doesn't know the type of variable to which a void pointer is pointing..but what i thought that,since void can point to any variable type so if we assign a void pointer to any pointer of some other type like :
{
void *p;
int *p1;
*p1=5;
p=p1;
/*now p points to p1(an integer type))*/
/*so*/
printf("%d",*p) ;/*will this statement work*/
}
so i am having this doubt....that is this the way to
dereference a void pointer...

[donbock]

No. The assignment operator transfers the value of p1 to p but it does not change the type of p. p is still a void pointer.

The assignment does work in the other direction:

int a;
void *p;
int *p1;
...
p = &a;
p1 = (int *)p;
*p1 = 10;

The cast on line 6 is optional in C, but it is required for C++.