HP C A.06.05 Reference Manual

Expressions and Operators

Function Calls

Chapter 5106

Function Calls

Syntax

postfix-expression ( [argument-expression-list] )

Description

Function calls provide a means of invoking a function and passing arguments to it.

The postﬁx-expression must have the type “pointer to function returning T”. The result of the

function will be type T. Functions can return any type of object except array and function.

Speciﬁcally, functions can return structures. In the case of structures, the contents of the

returned structure is copied to storage in the calling function. For large structures, this can

use a lot of execution time.

Although the expression denoting the called function must actually be a pointer to a function,

in typical usage, it is simply a function name. This works because the function name will

automatically be converted to a pointer.

C has no call statement. Instead, all function references must be followed by parentheses. The

parentheses contain any arguments that are passed to the function. If there are no

arguments, the parentheses must still remain. The parentheses can be thought of as a postﬁx

call operator.

If the function name is not declared before it is used, the compiler enters the default

declaration:

extern int

identifier

();

Function Arguments

Function arguments are expressions. Any type of object can be passed to a function as an

argument. Speciﬁcally, structures can be passed as arguments. Structure arguments are

copied to temporary storage in the called function. The length of time required to copy a

structure argument depends upon the structure's size.

If the function being called has a prototype, each argument is evaluated and converted as if

being assigned to an object of the type of the corresponding parameter. If the prototype has an

ellipsis, any argument speciﬁed after the ﬁxed parameters is subject to the default argument

promotions described below.