Zilog ZUSBOPTS - Manual (Page 482)

Standard Functions UM017105-0511
454
Zilog Developer Studio II – ZNEO™
User Manual
Synopsis
#include

type va_arg(va_list ap, type);
Returns
The first invocation of the va_arg macro after that of the va_start macro returns the
value of the argument after that specified by parmN. Successive invocations return the val-
ues of the remaining arguments in succession.
Example
The function f1 gathers into an array a list of arguments that are pointers to strings (but not
more than MAXARGS arguments), then passes the array as a single argument to function
f2. The number of pointers is specified by the first argument to f1.
#include
extern void f2(int n, char *array[]);
#define MAXARGS 31

void f1(int n_ptrs,...) {

va_list ap;

char *array[MAXARGS];

int ptr_no = 0;
if (n_ptrs > MAXARGS)

n_ptrs = MAXARGS;
va_start(ap, n_ptrs);
while (ptr_no < n_ptrs)

array[ptr_no++] = va_arg(ap, char *);
va_end(ap);

f2(n_ptrs, array);
}
Each call to f1 has in scope the definition of the function of a declaration such as void
f1(int, ...);
va_end
Facilitates a normal return from the function whose variable argument list was referenced
by the expansion of
va_start that initialized the va_list ap . The va_end function
can modify ap so that it is no longer usable (without an intervening invocation of
va_start ). If the va_end function is not invoked before the return, the behavior is unde-
fined.