HP C/iX Library Reference Manual (30026-90004)

30 Chapter4
HP C/iX Library Header Descriptions
Library Functions and Header File Macros
Library Functions and Header File Macros
The HP C/iX library contains both functions and macros. Macros improve the execution
speed of certain frequently used operations. One drawback to using macros is that they do
not have an address. For example, if a function expects the address of (a pointer to)
another function as an argument, you cannot use a macro name in that argument. The
following example illustrates the drawback:
#define add1(x) ((x)+=1)
extern f(void some_function( ));
main(void)
{
⋮
f(add1); /* This construct is illegal. */
⋮
}
Using add1 as an argument causes an error. To override a possible macro and ensure that
a library function is referenced as a true function, you can do any of the following:
• Use the #undef directive, which causes the function name to no longer be defined as a
macro.
• Enclose the function name in parentheses to suppress macro expansion.
• Take the address of the function using the & operator.
There are three ways in which a function can be declared:
• In a header file (which might generate a macro). This is the safest method to declare a
standard library function.
#include <stdlib.h>
m=abs(n);
• By explicit declaration. Make sure that your declaration matches the one in this
manual.
extern int abs(int j);
m=abs(n);
• By implicit declaration, if the function return type is int.
m=abs(n);