C storage type and static and storage type

Four Storage Class delimiters of C:
Extern: external variable
Static: static
Register: Memory
Auto: automatic

 

Static local variables:
The storage area and global variables are the same. The main difference between static local variables and global variables is that static local variables are only known for the blocks declared in them.
Static global variables:
Tells the compiler to create a global variable that is known only in the file that declares it. This means that even if the variable is global, the routines in other files may not know it or directly change its content, which avoids side effects.

Register: stores the value of a variable in the CPU register rather than in the memory. This modifier applies only to form parameters in local variables and functions, and does not allow global register variables.