Member functions can be defined within the class definition or separately using scope resolution operator, : −. Defining a member function within the class definition declares the function inline, even if you do not use the inline specifier. So either you can define Volume() function as below:

#ifndef CLASS_NAME_H # define CLASS_NAME_H class Sample { public: std::string str; void getStr(std::string str) { std::cout << str << std::endl; } Sample(void); ~Sample(void); }; #endif