Question 15.5

How can I write a function that takes a format string and a variable number of arguments, like printf, and passes them to printf to do most of the work?

Use vprintf, vfprintf, or vsprintf.

Here is an error routine which prints an error message, preceded by the string ``error: '' and terminated with a newline:

#include <stdio.h>
#include <stdarg.h>

void error(char *fmt, ...)
{
	va_list argp;
	fprintf(stderr, "error: ");
	va_start(argp, fmt);
	vfprintf(stderr, fmt, argp);
	va_end(argp);
	fprintf(stderr, "\n");
}