As shown in figure, books on the topic, the key is private I don't know how to implement, Internet is said to use local variables, but not understand

CodePudding user response:

Variables and functions can not access and use

CodePudding user response:

reference 1st floor qq_46221910 response:

variables and functions can not access and use?

The book says it is safer

CodePudding user response:

It use namespace STD is a namespace