Functions (Part 3)

Continuing with the previous post, today we will further go into details about functions.

Attributes of  a Variable:

All variables have attribute,which include;

  and;

–Scope

•Where variable can be referenced in program

–Storage class

•How long variable exists in memory

Storage Classes:

Thee are two storage classes:

–Automatic

–Static

Automatic Storage Classes:

Automatic storage class are either auto or register

–Variable created when program enters block in which it is defined

–Variable destroyed when program leaves block

–Local variables of functions are automatic

•Automatic by default

•keyword auto explicitly declares automatic

–register keyword

•Hint to place variable in high-speed register

•Good for often-used items (loop counters)

•Often unnecessary, compiler optimizes on its own

–Specify either register or auto, not both

•register int counter = 1;

Static Storage Classes:

In static storage class;

–Variables exist for entire program

•For functions, name exists for entire program

–Not accessible outside one file, scope rules still apply

•static keyword

–Local variables

–Keeps value between function calls

–Only known in own function

•extern keyword

–Default for global variables/functions

•Globals: defined outside of a function block

–Known in any function that comes after it

Scope Rules:

Scope is the portion of program where identifier can be used, it has further four categories

•File scope aka Global scope

–Defined outside a function, known in all functions

–Global variables, function definitions and prototypes

•Function scope

–Labels are the only identifiers with function scope

–Can only be referenced inside defining function

–Only labels, e.g., identifiers with a colon (case:)

–Labels used with ‘goto’ statement

•Block scope/Local scope

–Begins at declaration, ends at right brace }

•Can only be referenced in this range

–Local variables, function parameters

–static variables still have block scope

•Storage class separate from scope

•Function-prototype scope

–Parameter list of prototype

–Names in prototype optional

•Compiler ignores

–In a single prototype, name can be used only once

Functions with Empty Parameter Rules:

In c++ we often encounter functions with Empty parameter lists;

–void or leave parameter list empty

–Indicates function takes no arguments

–Function print takes no arguments and returns no value

•void print();

•void print( void );

Inline Functions:

Inline functions are a very useful in programming, if we know where to use them; 

–Keyword inline before function

–Asks the compiler to copy code into program instead of making function call

•Reduce function-call overhead

•Compiler can ignore inline

–Good for small, often-used functions

•Example

inline double cube( const double s )

{ return s * s * s; }

–const tells compiler that function does not modify s