'void *'不是指向对象的指针类型

Question

struct limit{
  int up;
  int down;
};

void *x;

struct limit *l;
l->up=1;
l->down=20;

x=l;

cout<<x->up;

This is part of my code I am getting error in last line 'void*' is not a pointer-to-object type . I know last line in my code is wrong. I just want to know how to print up and down values using x variable.

Answer 1

In this part:

struct limit *l;
l->up=1;
l->down=20;

you are dereferencing uninitialized pointer l , which results in undefined behavior . However, even if you initialized it properly, after you assign it to void* , you can not dereference void pointer:

void* x = l;
cout<< x->up;

you need to explicitly cast it back to struct limit* :

void* x = l;
struct limit * y = static_cast<struct limit*>(x);
cout << y->up;

or yet even better: avoid using void* at first place.

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Since you mentioned that you're doing this because of pthreads , then this answer will help you :)