varargs(3)varargs(3)Namevarargs - variable argument list
Syntax
#include <varargs.h>
function(va_alist)
va_dcl
va_list pvar;
va_start(pvar);
f = va_arg(pvar, type);
va_end(pvar);
Description
This set of macros provides a means of writing portable procedures that
accept variable argument lists. Routines having variable argument
lists, such as that do not use varargs are inherently nonportable,
since different machines use different argument passing conventions.
va_alist is used in a function header to declare a variable argument
list.
va_dcl is a declaration for va_alist. Note that there is no semicolon
after va_dcl.
va_list is a type which can be used for the variable pvar, which is
used to traverse the list. One such variable must always be declared.
va_start(pvar) is called to initialize pvar to the beginning of the
list.
va_arg(pvar, type) will return the next argument in the list pointed to
by pvar. The type is the type the argument is expected to be. Differ‐
ent types can be mixed, but it is up to the routine to know what type
of argument is expected, since it cannot be determined at runtime.
va_end(pvar) is used to finish up.
Multiple traversals, each bracketed by va_start ... va_end, are possi‐
ble.
Examples
#include <varargs.h>
execl(va_alist)
va_dcl
{
va_list ap;
char *file;
char *args[100];
int argno = 0;
va_start(ap);
file = va_arg(ap, char *);
while (args[argno++] = va_arg(ap, char *))
B;
va_end(ap);
return execv(file, args);
}
Restrictions
It is up to the calling routine to determine how many arguments there
are, since it is not possible to determine this from the stack frame.
For example, passes a 0 to signal the end of the list. The command can
tell how many arguments are supposed to be there by the format.
varargs(3)
