stdarg.h——变长参数的真相

 

#ifndef _STDARG_H
#define _STDARG_H
typedef char *va_list;
/* Amount of space required in an argument list for an arg of type TYPE.
   TYPE may alternatively be an expression whose type is used.  */
#define __va_rounded_size(TYPE)  \
  (((sizeof (TYPE) + sizeof (int) - 1) / sizeof (int)) * sizeof (int))
#ifndef __sparc__
#define va_start(AP, LASTARG)       \
 (AP = ((char *) &(LASTARG) + __va_rounded_size (LASTARG)))
#else
#define va_start(AP, LASTARG)       \
 (__builtin_saveregs (),      \
  AP = ((char *) &(LASTARG) + __va_rounded_size (LASTARG)))
#endif
void va_end (va_list);  /* Defined in gnulib */
#define va_end(AP)
#define va_arg(AP, TYPE)      \
 (AP += __va_rounded_size (TYPE),     \
  *((TYPE *) (AP - __va_rounded_size (TYPE))))
#endif /* _STDARG_H */