GNU C Library (libc) Programming Guide - How Variadic

A.2.2 How Variadic Functions are Defined and Used

Defining and using a variadic function involves three steps:

• Define the function as variadic, using an ellipsis (`...') in the argument list, and using special macros to access the variable arguments. See Receiving Arguments.
• Declare the function as variadic, using a prototype with an ellipsis (`...'), in all the files which call it. See Variadic Prototypes.
• Call the function by writing the fixed arguments followed by the additional variable arguments. See Calling Variadics.

• Variadic Prototypes: How to make a prototype for a function with variable arguments.
• Receiving Arguments: Steps you must follow to access the optional argument values.
• How Many Arguments: How to decide whether there are more arguments.
• Calling Variadics: Things you need to know about calling variable arguments functions.
• Argument Macros: Detailed specification of the macros for accessing variable arguments.
• Old Varargs: The pre-ISO way of defining variadic functions.