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

// posix
int main() {

	int fd = open("a.txt", O_CREAT | O_RDWR);

	char *buffer = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
	
	write(fd, buffer, strlen(buffer));

	char rbuffer[128] = {0};
	read(fd, buffer, 128);

	printf("rbuffer: %s\n", buffer);

	close(fd);
}