CS 3733 Operating Systems Notes: Storage and Linkage Classes

Storage classes: static and automatic

• static storage class refers to variables that, once allocated, persist throughout the execution of a program.
• automatic storage class refers to variables which come into existence when the block in which they are declared is enteredand are discarded when the defining block is exited.
• Variables declared inside a function have automatic storage class unless they are declared to be static.
  These are usually allocated on the program stack.
• Variables defined outside any funtions have static storage class.

Linkage class determines whether variables can be accessed in files other than the one in which they are declared.

• Internal linkage class means they can only be accessed in the file in which they are declared.
• External linkage class means they can be accessed in other files.
• variables decalred outside and function and function name identifiers have external linkage by default.
  They can be given internal linkage with the key word static.
• Varibales decalred inside a function are only known inside that function and so have internal linkage.