c++ - Why copy constructor and assignment operator are disallowed?

Question

#undef GOOGLE_DISALLOW_EVIL_CONSTRUCTORS
#define GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(TypeName)    
   TypeName(const TypeName&);                           
   void operator=(const TypeName&)

I'm, reading open source code from google. Why copy constructor and assignment operator are disallowed?

Answer 1

To prevent instances of the class being copied or assigned. Most classes should not allow copying. Consider for example a BankAccount class - if you are writing software for a bank, they will not be too happy if you create copies of accounts and then apply credits and debits to those different copies.