C++ Const Keyword in Member Function

在宣告類別時，const修飾成員函式，表示呼叫該成員函式時不會修改到物件內容。

class name{
  access limit:
   return type FunctionMemeber(argumentType argumentName,..) const;
   ...
};

const 物件可以呼叫const成員函式，不可呼叫non-const成員函式
non-const物件可以呼叫const與non-const成員函式

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Illustrate

Picture1. const member function definition

Picture2. lhs defined as const object can call const Get() member function

Picture3. lhs defined as non-const object can call const Get() member function

Conclusion:
宣告成const成員函式，就可讓const, non–const物件來呼叫!

Reference codes from GitHub:
dataStructure/returnobject.cpp