testapp.c

#include <stdio.h>
#include <fcntl.h> 
#include <stdlib.h>

int main(int argc, char *argv[])
{
    char buffer[1024];	
	int fd;
	int length;

	fd = open("/dev/msg", O_RDWR);
	if (fd < 0) {
		perror("fd failed");
		exit(2);
	}
	printf("write : %d\n", write(fd, "hello world", sizeof("hello world")));	
	length = read(fd, buffer, sizeof(buffer));
	buffer[length] = '\0';
	printf("Read:%s\n", buffer);
	memset(buffer, 0, sizeof(buffer));
	length = read(fd, buffer, sizeof(buffer));
	buffer[length] = '\0';
	printf("Read:%s\n", buffer);
	close(fd);
}