HP C/iX Reference Manual (31506-90011)

52 Chapter3
Data Types and Declarations
Function Definitions
Function Definitions
A function definition introduces a new function.
Syntax
function-definition ::=
[declaration-specifiers] declarator [declaration-list] compound-statement
Description
A function definition provides the following information about the function:
1. Type. You can specify the return type of the function. If no type is provided, the default
return type is int. If the function does not return a value, it can be defined as having a
return type of void. You can declare functions as returning any type except a function
or an array. You can, however, define functions that return pointers to functions or
pointers to arrays.
2. Formal parameters. There are two ways of specifying the type and number of the
formal parameters to the function:
a. A function declarator containing an identifier list
The identifiers are formal parameters to the function. You must include at least one
declarator for each declaration in the declaration list of the function. These
declarators declare only identifiers from the identifier list of parameters. If a
parameter in the identifier list has no matching declaration in the declaration list,
the type of the parameter defaults to int.
b. A function declarator containing a parameter type list (prototype form).
In this case, the function definition cannot include a declaration list. You must
include an identifier in each parameter declaration (not an abstract declarator). The
one exception is when the parameter list consists of a single parameter of type void;
in this case do not use an identifier.
NOTE Function prototypes can be used only in ANSI mode.
3. Visibility outside defining translation unit. A function can be local to the
translation unit in which it is defined (if the storage class specifier is static).
Alternatively, a function can be visible to other translation units (if no storage class is
specified, or if the storage class is extern).
4. Body of the function. You supply the body that executes when the function is called
in a single compound statement following the optional
declaration-list.
Do not confuse definition with declaration, especially in the case of functions. Function
definition implies that the above four pieces of information are supplied. Function
declaration implies that the function is defined elsewhere.