stdarg.h in C

• stdarg.h is a header in the C standard library of the C programming language that allows functions to accept an indefinite number of arguments. It provides facilities for stepping through a list of function arguments of unknown number and type. C++ provides this functionality in the header cstdarg.

• The contents of stdarg.h are typically used in variadic functions, though they may be used in other functions (for example, vprintf) called by variadic functions.

•  stdarg.h header defines a variable type va_list and three macros which can be used to get the arguments in a function when the number of arguments are not known i.e. variable number of arguments. 

Library Variables

•  va_list

This is a type suitable for holding information needed by the three macros va_start(), va_arg() and va_end().

Library Macros

	void va_start(va_list ap, last_arg) This macro initializes ap variable to be used with the va_arg and va_end macros. The last_arg is the last known fixed argument being passed to the function i.e. the argument before the ellipsis.
	type va_arg(va_list ap, type) This macro retrieves the next argument in the parameter list of the function with type type.
	void va_end(va_list ap) This macro allows a function with variable arguments which used the va_start macro to return. If va_end is not called before returning from the function, the result is undefined.

 

 Example :

more at : 
https://en.wikipedia.org/wiki/Stdarg.h

 http://www.tutorialspoint.com/c_standard_library/stdarg_h.htm