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