reading a file that doesn't exist

[john eipe]

Hi,

I have got a small program that prints the contents of files using the system call - read.

	unsigned char buffer[8];
	size_t offset=0;
	size_t bytes_read;

	int i;

	int fd = open(argv[1], O_RDONLY);
	
	do{
		bytes_read = read(fd, buffer, sizeof(buffer));
		printf("0x%06x : ", offset);
	
		for(i=0; i<bytes_read; ++i)
		{
			printf("%c ", buffer[i]);
		}
		printf("\n");
		offset = offset + bytes_read;
	}while(bytes_read == sizeof(buffer));

Now while running I give a file name that doesn't exist.
It prints some kind of data mixed with environment variables and a segmentation fault at the end.

How is this possible? What is the program printing?

[horace1]

you should check that the file opened OK

   int fd = open(argv[1], O_RDONLY);

otherwise when you attempt to read you get rubblish or segmentation faults, see

http://www.cprogramming.com/tutorial/cfileio.html