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

void main(){
	int fd = open("testfile", O_RDWR);
	char *file_area = mmap(0, 1024, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
	printf("%s\n", file_area);
	file_area[10] = 'Z';
	int len = strlen(file_area);

	file_area[len] = 'Z'; // If you actually want to append, use write, with O_APPEND
	file_area[len+1] = 'Z'; // If you actually want to append, use write, with O_APPEND
	file_area[len+2] = 0;
	printf("%s\n", file_area);

	msync(file_area, 1024, MS_SYNC);
	munmap(file_area, 1024);
	close(fd);
}