Defective * needed separately from memory related items

Question

Is it void*necessary, in addition to material related to memory allocation, in C ++? Can you give me an example?

Answer 1

Addressing memory addresses

If you want to display a pointer using iostreams (for example, for logging), then going through void*is the only way to ensure that it operator<<doesn't get overloaded in some crazy way.

#include <iostream>

struct foo {
};

std::ostream& operator<<(std::ostream& out, foo*) {
  return out<<"it a trap!";
}

int main() {
  foo bar;
  foo *ptr = &bar;

  std::cout << ptr << std::endl;
  std::cout << static_cast<void*>(ptr) << std::endl;
}

---

Testing iostream status

iostreams overloads operator void*as a status check, so syntax like if (stream)or while (stream)is a short way to check the status of a stream.

---

-

, void* , , . SFINAE, , , , .

---

, dynamic_cast<void*> , :

#include <iostream>

struct other {
  virtual void func() = 0;
  int c;
};

struct foo {
  virtual void func() { std::cout << "foo" << std::endl; }
  int a;
};

struct bar : foo, other {
  virtual void func() { std::cout << "bar" << std::endl; }
  int b;
};

namespace {
  void f(foo *ptr) {
    ptr->func();
    std::cout << ptr << std::endl;
    std::cout << dynamic_cast<void*>(ptr) << std::endl;
  }

  void g(other *ptr) {
    ptr->func();
    std::cout << ptr << std::endl;
    std::cout << dynamic_cast<void*>(ptr) << std::endl;
  }
}

int main() {
  foo a;
  bar b;
  f(&a);
  f(&b);
  g(&b);
}

:

foo
0xbfb815f8
0xbfb815f8
bar
0xbfb815e4
0xbfb815e4
bar
0xbfb815ec
0xbfb815e4

.

---

§ 15.3.1 :

, void *, const void*, volatile void * const volatile void *.

, void*. ( , , )

---

Legacy C

"" C void* , , , ++ .

Answer 2

( C).

( ). , (, ). , , . void*, .

Answer 3

void* .

C, , void .

[]

, , , .

Answer 4

, .

Answer 5

, , , void, - , , :

void loadData(void* data, std::size_t size)

char -pointer void, , , 1 , , , , ++ char .

void . : " , , ". , .

Answer 6

void * ++ .

, , , :

• ...

void * , , .

,

template <typename T>
class vector {
 /*stuff */
};

T *, void, .