[c/c++] file copy using 'sendfile' on linux.

Since Linux 2.6.33, sendfile supports regular file as output file.
That is, sendfile can be used as way for fast file copy.
(Faster than normal read -> write operation because it is done inside kernel! )
Please refer follow example code ...

...

#include <stdio.h>
#include <sys/sendfile.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int
main(int argc, const char *argv[]) {
	int ifd, ofd, r;
	struct stat st;

	r = stat(argv[2], &st);
	r |= (ofd = open(argv[1], O_WRONLY | O_CREAT));
	r |= (ifd = open(argv[2], O_RDONLY));
	if (r < 0)
		return 1;
	if (-1 == sendfile(ofd, ifd, 0, st.st_size))
		return 1;
	fchmod(ofd, 0664);
	return 0;
}

...