const_cast

struct type
{
    int i;
 
    type(): i(3) {}
 
    void f(int v) const
    {
        // this->i = v;                 // compile error: this is a pointer to const
        const_cast<type*>(this)->i = v; // OK as long as the type object isn't const
    }
};
 
int main() 
{
    int i = 3;                 // i is not declared const
    const int& rci = i;         // const reference
    const_cast<int&>(rci) = 4; // OK: modifies i
    std::cout << "i = " << i << '\n';
    
    const int* pci = &i;
    // *pci = 5;                   // error: assignment of read-only location ‘* pci’
    *const_cast<int*>(pci) = 5; // OK: modifies i
    std::cout << "i = " << i << '\n';
 
    type t; // if this was const type t, then t.f(4) would be undefined behavior
    t.f(4);
    std::cout << "type::i = " << t.i << '\n';
 
    const int j = 3; // j is declared const
    int* pj = const_cast<int*>(&j);
    // *pj = 4;      // undefined behavior
    
    const int& r2 = j; // 绑定到 const 对象的 const 引用
    const_cast<int&>(r2) = 2; // 未定义行为：试图修改 const 对象 j
    
    void (type::*pmf)(int) const = &type::f; // pointer to member function
    // const_cast<void(type::*)(int)>(pmf);   // compile error: const_cast does
                                              // not work on function pointers
    (t.*pmf)(40);
}

i = 4
i = 5
type::i = 4
type::i = 40