Other storage classes
There are three more storage class identifiers in C:
autois the opposite of
static. It is redundant, but is included in contemporary versions of C for backwards compatibility. All local variables are
registeris another outdated C storage class. Defining a variable as
registerused to store it in one of the computer's registers, a specific location on its processor chip, thereby making code using that variable run faster. These days, most C compilers (including GCC) are smart enough to optimize the code (make it faster and more compact) without the
typedefallows you to define your own variable types. See More data types, for more information.