C Language-Keywords

1volatile: variable, general register access speed is faster than RAM, so after the optimization is specified, the general compiler will read the data from the register to speed up.

And for: State information determined by the hardware register device, etc.

The variable flags that are modified in the interrupt service program and are ultimately used by other program queries, such as: Key values, soft-timed times, etc.

Multi-threaded shared variables

Should be modified with a volatile modifier to allow the compiler to read data from the variable's defined address at the same time to prevent an error.

2 extern: Common functions can be used or not, because the function itself defaults to common properties, and variables are used to prevent redefinition

C Language-Keywords