转换为无效*

Question

how can I convert any object of my own class convert into pointer to void?

MyClass obj;
(void*)obj; // Fail

Answer 1

MyClass obj;
void *p;

p = (void*)&obj; // Explicit cast.
// or:
p = &obj; // Implicit cast, as every pointer is compatible with void *

But beware ! obj is allocated on the stack this way, as soon as you leave the function the pointer becomes invalid.

Edit : Updated to show that in this case an explicit cast is not necessary since every pointer is compatible with a void pointer.

Answer 2

If you use the address, you can convert it to a void pointer.

MyClass obj;
void *ptr = (void*)&obj; // Success!

Answer 3

You cant convert a non-pointer to void* . You need to convert the pointer to your object to void*

(void*)(&obj); //no need to cast explicitly.

that conversion is implicit

void* p = &obj; //OK

Answer 4

To do something which has any chance of being meaningful, first you have to take the address of an object, obtaining a pointer value; then cast the pointer.

MyClass obj;
MyClass * pObj = &obj;
void * pVoidObj = (void*)pObj;

Answer 5

i beleive you could only convert a pointer to an object to a pointer to void???

Perhaps: (void*)(&obj)

Answer 6

In addition to the technical answers: Assert, that you avoid multiple inheritance or else you don't assign the address of super-class interfaces to a void*, for they will not be unique. Eg

class S1 { int u; };
class S2 { int v; };
class MyClass : public S1, public S2 {};

MyClass obj;
S2* s2 = &obj;
void * p1 = &obj;
void * p2 = s2;

Here p1 and p2 (==s2) will be different, because the S2 instance in C has an address offset.