C++ Assignment operator vs _BLOCK_TYPE_IS_VALID

I have been using C++ for a long time, but I didn't pay much attention to the assignment operator and copy constructor until I encountered the "_BLOCK_TYPE_IS_VALID" error.
It took me several hours of googling to figure out the reason.
with this code:

class A { int* val; public: A(int v) { val = new int(v); } ~A() { delete val; }; A test() { A a(2); A b(3); a = b;// assignment operator return a; } 

we got the "_BLOCK_TYPE_IS_VALID" because when the class does not contain any pointers, the default assignment provided by Compiler is sufficient even it just performs a shadow copy.
but dealing with classes that contain pointers we can get _BLOCK_TYPE_IS_VALID(pHead->nBlockUse).
This error often occurs in Visual Studio when memory corruption or invalid memory access is encountered.
Similarly, in a Linux environment, you may encounter dump values or other exceptions.

so do not forget to define our own assignment operator.

class A{ int* val; public: A(int v){ val = new int(v); } // assignment operator A& operator=(const A& obj){ *val = *obj.val; } ~A(){ delete val;) }; A test(){ A a(2); A b(3); a = b;// assignment operator called return a; // copy constructor ?? } 

but still we got error?. because the return a; make a copy of a before return.
so we also need our own copy constructor
and this code will work without error:

class A{ int* val; public: A(int v){ val = new int(v); } // assignment operator A& operator=(const A& obj){ *val = *obj.val; } //copy constructor A(const A& obj){ if(val) delete val; val = new int(*obj.val); } ~A(){ delete val;) }; A test(){ A a(2); A b(3); a = b;// assignment operator called return a; // copy constructor ?? }