7.15 Variable arguments <stdarg.h>

• 7.15.1 Variable argument list access macros
  • 7.15.1.1 The va_arg macro
  • 7.15.1.2 The va_copy macro
  • 7.15.1.3 The va_end macro
  • 7.15.1.4 The va_start macro

1

The header <stdarg.h> declares a type and defines four macros, for advancing through a list of arguments whose number and types are not known to the called function when it is translated.

2

A function may be called with a variable number of arguments of varying types. As described in 6.9.1, its parameter list contains one or more parameters. The rightmost parameter plays a special role in the access mechanism, and will be designated parmN in this description.

3

The type declared is

va_list

which is an object type suitable for holding information needed by the macros va_start, va_arg, va_end, and va_copy. If access to the varying arguments is desired, the called function shall declare an object (generally referred to as ap in this subclause) having type va_list. The object ap may be passed as an argument to another function; if that function invokes the va_arg macro with parameter ap, the value of ap in the calling function is indeterminate and shall be passed to the va_end macro prior to any further reference to ap.[1]

Footnotes

[1]

It is permitted to create a pointer to a va_list and pass that pointer to another function, in which case the original function may make further use of the original list after the other function returns.