fdprintf.c

#include <unistd.h>
#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>

int vfdprintf(int fd, const char *fmt, va_list ap)
{
	va_list args;
	char *str = NULL;
	va_copy(args, ap);
	int size = vsnprintf(NULL, 0, fmt, args) + 1; /* For '\0' */

	/* if negative number is returned return error */
	if(size < 0)
		return -1;
	str = (char *)malloc(size);
	if(str == NULL)
		return -1;
	va_end(args);
	vsprintf(str, fmt, ap);
     write(fd, str, size + 1);
	free(str);
	return size;
} 

int
fdprintf(int fd, const char *fmt, ...)
{
	va_list args;
	int size = 0;
	va_start(args, fmt);
	size = vfdprintf(fd,fmt,args);
	va_end(args);
	return size;
}

int
main(void)
{
	int fd = open("hello.txt",O_RDWR);
	fdprintf(fd,"hello world %i %s %X\n", 42, "spurdo sparde", 2147483647);
	return 0;
}