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#include <varargs.h>va_alist
va_dcl
va_list pvar;
void va_start(va_list pvar);
type va_arg(va_list pvar, type);
void va_end(va_list pvar);
va_alist is used as the parameter list in a function header.
va_dcl is a declaration for va_alist. No semicolon should follow va_dcl.
va_list is a type defined for the variable used to traverse the list.
va_start is called to initialize pvar to the beginning of the list.
va_arg will return the next argument in the list pointed to by pvar. type is the type the argument is expected to be. Different types can be mixed, but it is up to the routine to know what type of argument is expected, as it cannot be determined at runtime.
va_end is used to clean up.
Multiple traversals, each bracketed by va_start and va_end, are possible.
#include <unistd.h> #include <varargs.h> #define MAXARGS 100/ execl is called by execl(file, arg1, arg2, . . ., (char )0); / execl(va_alist) va_dcl { va_list ap; char file; char args[MAXARGS]; / assumed big enough/ int argno = 0;
va_start(ap); file = va_arg(ap, char ); while ((args[argno++] = va_arg(ap, char )) != 0) ; va_end(ap); return execv(file, args); }
It is non-portable to specify a second argument of char, short, or float to va_arg, since arguments seen by the called function are not char, short, or float. C converts char and short arguments to int and converts float arguments to double before passing them to a function.
stdarg is the preferred interface.