About the variable parameter list

A variable argument list allows a function to receive different numbers of arguments at different times, and the most typical example is printf ().

Now let's take a look at how to implement a printf function in the simplest way.

First, the header file:

#include <stdarg.h>

After the Stdarg.h header file is included, we can use the following macros:

Va_start, Va_end

There are also data types:

Va_list

Specifically implemented as follows:

1 void my_printf (char *fmt, ...)
2 {
3 va_list list;
4 Va_start (list, FMT);
5 vprintf (FMT, list);
6 va_end (list);
7}

Va_start is used to initialize so that the list points to the first argument after FMT.

Va_end is called when the use is complete.