C ++ keywords

C ++ keywords

Asm	Double	New	Switch
Auto	Else	Operator	Template
Break	Enum	Private	This
Case	Extern	Protected	Throw
Catch	Float	Public	Try
Char	For	Return	Typedef
Class	Friend	Register	Union
Const	Goto	Short	Unsigned
Continue	If	Signed	Virtual
Default	Inline	Sizeof	Void
Delete	Int	Static	Volatile
Do	Long	Struct	While

The red part is unique to C ++, and the black part is a common part of C ++ and C.

Key Parts:

VolatileUsage:

1) Hardware registers of parallel Devices

2) Non-automatic variables that will be accessed in a terminal service subroutine

3) variables shared by several tasks in multi-threaded applications

In this thread, when reading a variable, in order to improve the access speed, the compiler sometimes first reads the variable to a register during optimization. When the variable value is obtained later, the value is taken directly from the register. When the value of a variable changes in the current thread, the new value of the variable is copied to the register at the same time to maintain consistency. However, when the value of a variable is changed due to other threads, the value of this register will not change accordingly, resulting in inconsistent values read by the application and the actual value of the variable.